perf_event_open — set up performance monitoring
#include <linux/perf_event.h> #include <linux/hw_breakpoint.h>
int
perf_event_open( |
struct perf_event_attr *attr, |
| pid_t pid, | |
| int cpu, | |
| int group_fd, | |
unsigned long flags); |
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Note |
|---|---|
| There is no glibc wrapper for this system call; see NOTES. |
Given a list of parameters, perf_event_open() returns a file
descriptor, for use in subsequent system calls (read(2), mmap(2), prctl(2), fcntl(2), etc.).
A call to perf_event_open()
creates a file descriptor that allows measuring performance
information. Each file descriptor corresponds to one event
that is measured; these can be grouped together to measure
multiple events simultaneously.
Events can be enabled and disabled in two ways: via ioctl(2) and via prctl(2). When an event is disabled it does not count or generate overflows but does continue to exist and maintain its count value.
Events come in two flavors: counting and sampled. A
counting event is
one that is used for counting the aggregate number of events
that occur. In general, counting event results are gathered
with a read(2) call. A sampling event periodically
writes measurements to a buffer that can then be accessed via
mmap(2).
The pid and
cpu arguments allow
specifying which process and CPU to monitor:
This measures the calling process/thread on any CPU.
This measures the calling process/thread only when running on the specified CPU.
This measures the specified process/thread on any CPU.
This measures the specified process/thread only when running on the specified CPU.
This measures all processes/threads on the
specified CPU. This requires CAP_SYS_ADMIN capability or a
/proc/sys/kernel/perf_event_paranoid
value of less than 1.
This setting is invalid and will return an error.
When pid is
greater than zero, permission to perform this system call
is governed by a ptrace access mode PTRACE_MODE_READ_REALCREDS check; see
ptrace(2).
The group_fd
argument allows event groups to be created. An event group
has one event which is the group leader. The leader is
created first, with group_fd = −1. The rest
of the group members are created with subsequent
perf_event_open() calls with
group_fd being set
to the file descriptor of the group leader. (A single event
on its own is created with group_fd = −1 and is
considered to be a group with only 1 member.) An event
group is scheduled onto the CPU as a unit: it will be put
onto the CPU only if all of the events in the group can be
put onto the CPU. This means that the values of the member
events can be meaningfully compared—added, divided
(to get ratios), and so on—with each other, since
they have counted events for the same set of executed
instructions.
The flags
argument is formed by ORing together zero or more of the
following values:
PERF_FLAG_FD_CLOEXEC (since Linux
3.14)This flag enables the close-on-exec flag for the
created event file descriptor, so that the file
descriptor is automatically closed on execve(2). Setting
the close-on-exec flags at creation time, rather than
later with fcntl(2), avoids
potential race conditions where the calling thread
invokes perf_event_open() and fcntl(2) at the
same time as another thread calls fork(2) then
execve(2).
PERF_FLAG_FD_NO_GROUPThis flag tells the event to ignore the group_fd parameter
except for the purpose of setting up output
redirection using the PERF_FLAG_FD_OUTPUT flag.
PERF_FLAG_FD_OUTPUT (broken since
Linux 2.6.35)This flag re-routes the event's sampled output to
instead be included in the mmap buffer of the event
specified by group_fd.
PERF_FLAG_PID_CGROUP (since Linux
2.6.39)This flag activates per-container system-wide
monitoring. A container is an abstraction that
isolates a set of resources for finer-grained control
(CPUs, memory, etc.). In this mode, the event is
measured only if the thread running on the monitored
CPU belongs to the designated container (cgroup). The
cgroup is identified by passing a file descriptor
opened on its directory in the cgroupfs filesystem.
For instance, if the cgroup to monitor is called
test, then
a file descriptor opened on /dev/cgroup/test (assuming cgroupfs
is mounted on /dev/cgroup) must be passed as the
pid
parameter. cgroup monitoring is available only for
system-wide events and may therefore require extra
permissions.
The perf_event_attr structure provides detailed configuration information for the event being created.
struct perf_event_attr { __u32 type; /* Type of event */ __u32 size; /* Size of attribute structure */ __u64 config; /* Type-specific configuration */ union { __u64 sample_period; /* Period of sampling */ __u64 sample_freq; /* Frequency of sampling */ }; __u64 sample_type; /* Specifies values included in sample */ __u64 read_format; /* Specifies values returned in read */ __u64 disabled : 1, /* off by default */ inherit : 1, /* children inherit it */ pinned : 1, /* must always be on PMU */ exclusive : 1, /* only group on PMU */ exclude_user : 1, /* don't count user */ exclude_kernel : 1, /* don't count kernel */ exclude_hv : 1, /* don't count hypervisor */ exclude_idle : 1, /* don't count when idle */ mmap : 1, /* include mmap data */ comm : 1, /* include comm data */ freq : 1, /* use freq, not period */ inherit_stat : 1, /* per task counts */ enable_on_exec : 1, /* next exec enables */ task : 1, /* trace fork/exit */ watermark : 1, /* wakeup_watermark */ precise_ip : 2, /* skid constraint */ mmap_data : 1, /* non-exec mmap data */ sample_id_all : 1, /* sample_type all events */ exclude_host : 1, /* don't count in host */ exclude_guest : 1, /* don't count in guest */ exclude_callchain_kernel : 1, /* exclude kernel callchains */ exclude_callchain_user : 1, /* exclude user callchains */ mmap2 : 1, /* include mmap with inode data */ comm_exec : 1, /* flag comm events that are due to exec */ use_clockid : 1, /* use clockid for time fields */ __reserved_1 : 38; union { __u32 wakeup_events; /* wakeup every n events */ __u32 wakeup_watermark; /* bytes before wakeup */ }; __u32 bp_type; /* breakpoint type */ union { __u64 bp_addr; /* breakpoint address */ __u64 config1; /* extension of config */ }; union { __u64 bp_len; /* breakpoint length */ __u64 config2; /* extension of config1 */ }; __u64 branch_sample_type; /* enum perf_branch_sample_type */ __u64 sample_regs_user; /* user regs to dump on samples */ __u32 sample_stack_user; /* size of stack to dump on samples */ __s32 clockid; /* clock to use for time fields */ __u64 sample_regs_intr; /* regs to dump on samples */ __u32 aux_watermark; /* aux bytes before wakeup */ __u32 __reserved_2; /* align to u64 */ };
The fields of the perf_event_attr structure are described in more detail below:
typeThis field specifies the overall event type. It has one of the following values:
PERF_TYPE_HARDWAREThis indicates one of the "generalized" hardware events provided by the kernel. See the
configfield definition for more details.PERF_TYPE_SOFTWAREThis indicates one of the software-defined events provided by the kernel (even if no hardware support is available).
PERF_TYPE_TRACEPOINTThis indicates a tracepoint provided by the kernel tracepoint infrastructure.
PERF_TYPE_HW_CACHEThis indicates a hardware cache event. This has a special encoding, described in the
configfield definition.PERF_TYPE_RAWThis indicates a "raw" implementation-specific event in the
configfield.PERF_TYPE_BREAKPOINT(since Linux 2.6.33)This indicates a hardware breakpoint as provided by the CPU. Breakpoints can be read/write accesses to an address as well as execution of an instruction address.
- dynamic PMU
Since Linux 2.6.38,
perf_event_open() can support multiple PMUs. To enable this, a value exported by the kernel can be used in thetypefield to indicate which PMU to use. The value to use can be found in the sysfs filesystem: there is a subdirectory per PMU instance under/sys/bus/event_source/devices. In each subdirectory there is atypefile whose content is an integer that can be used in thetypefield. For instance,/sys/bus/event_source/devices/cpu/typecontains the value for the core CPU PMU, which is usually 4.
sizeThe size of the perf_event_attr structure for forward/backward compatibility. Set this using sizeof(struct perf_event_attr) to allow the kernel to see the struct size at the time of compilation.
The related define PERF_ATTR_SIZE_VER0 is set to 64;
this was the size of the first published struct.
PERF_ATTR_SIZE_VER1 is
72, corresponding to the addition of breakpoints in
Linux 2.6.33. PERF_ATTR_SIZE_VER2 is 80
corresponding to the addition of branch sampling in
Linux 3.4. PERF_ATTR_SIZE_VER3 is 96
corresponding to the addition of sample_regs_user and
sample_stack_user in
Linux 3.7. PERF_ATTR_SIZE_VER4 is 104
corresponding to the addition of sample_regs_intr in
Linux 3.19. PERF_ATTR_SIZE_VER5 is 112
corresponding to the addition of aux_watermark in
Linux 4.1.
configThis specifies which event you want, in
conjunction with the type field. The
config1 and
config2
fields are also taken into account in cases where 64
bits is not enough to fully specify the event. The
encoding of these fields are event dependent.
There are various ways to set the config field that are
dependent on the value of the previously described
type field.
What follows are various possible settings for
config
separated out by type.
If type
is PERF_TYPE_HARDWARE,
we are measuring one of the generalized hardware CPU
events. Not all of these are available on all
platforms. Set config to one of the
following:
PERF_COUNT_HW_CPU_CYCLESTotal cycles. Be wary of what happens during CPU frequency scaling.
PERF_COUNT_HW_INSTRUCTIONSRetired instructions. Be careful, these can be affected by various issues, most notably hardware interrupt counts.
PERF_COUNT_HW_CACHE_REFERENCESCache accesses. Usually this indicates Last Level Cache accesses but this may vary depending on your CPU. This may include prefetches and coherency messages; again this depends on the design of your CPU.
PERF_COUNT_HW_CACHE_MISSESCache misses. Usually this indicates Last Level Cache misses; this is intended to be used in conjunction with the
PERF_COUNT_HW_CACHE_REFERENCESevent to calculate cache miss rates.PERF_COUNT_HW_BRANCH_INSTRUCTIONSRetired branch instructions. Prior to Linux 2.6.35, this used the wrong event on AMD processors.
PERF_COUNT_HW_BRANCH_MISSESMispredicted branch instructions.
PERF_COUNT_HW_BUS_CYCLESBus cycles, which can be different from total cycles.
PERF_COUNT_HW_STALLED_CYCLES_FRONTEND(since Linux 3.0)Stalled cycles during issue.
PERF_COUNT_HW_STALLED_CYCLES_BACKEND(since Linux 3.0)Stalled cycles during retirement.
PERF_COUNT_HW_REF_CPU_CYCLES(since Linux 3.3)Total cycles; not affected by CPU frequency scaling.
If type
is PERF_TYPE_SOFTWARE,
we are measuring software events provided by the
kernel. Set config to one of the
following:
PERF_COUNT_SW_CPU_CLOCKThis reports the CPU clock, a high-resolution per-CPU timer.
PERF_COUNT_SW_TASK_CLOCKThis reports a clock count specific to the task that is running.
PERF_COUNT_SW_PAGE_FAULTSThis reports the number of page faults.
PERF_COUNT_SW_CONTEXT_SWITCHESThis counts context switches. Until Linux 2.6.34, these were all reported as user-space events, after that they are reported as happening in the kernel.
PERF_COUNT_SW_CPU_MIGRATIONSThis reports the number of times the process has migrated to a new CPU.
PERF_COUNT_SW_PAGE_FAULTS_MINThis counts the number of minor page faults. These did not require disk I/O to handle.
PERF_COUNT_SW_PAGE_FAULTS_MAJThis counts the number of major page faults. These required disk I/O to handle.
PERF_COUNT_SW_ALIGNMENT_FAULTS(since Linux 2.6.33)This counts the number of alignment faults. These happen when unaligned memory accesses happen; the kernel can handle these but it reduces performance. This happens only on some architectures (never on x86).
PERF_COUNT_SW_EMULATION_FAULTS(since Linux 2.6.33)This counts the number of emulation faults. The kernel sometimes traps on unimplemented instructions and emulates them for user space. This can negatively impact performance.
PERF_COUNT_SW_DUMMY(since Linux 3.12)This is a placeholder event that counts nothing. Informational sample record types such as mmap or comm must be associated with an active event. This dummy event allows gathering such records without requiring a counting event.
If
typeisPERF_TYPE_TRACEPOINT, then we are measuring kernel tracepoints. The value to use inconfigcan be obtained from under debugfstracing/events/*/*/idif ftrace is enabled in the kernel.
If
typeisPERF_TYPE_HW_CACHE, then we are measuring a hardware CPU cache event. To calculate the appropriateconfigvalue use the following equation:(perf_hw_cache_id) | (perf_hw_cache_op_id << 8) | (perf_hw_cache_op_result_id << 16)where
perf_hw_cache_idis one of:
PERF_COUNT_HW_CACHE_L1Dfor measuring Level 1 Data Cache
PERF_COUNT_HW_CACHE_L1Ifor measuring Level 1 Instruction Cache
PERF_COUNT_HW_CACHE_LLfor measuring Last-Level Cache
PERF_COUNT_HW_CACHE_DTLBfor measuring the Data TLB
PERF_COUNT_HW_CACHE_ITLBfor measuring the Instruction TLB
PERF_COUNT_HW_CACHE_BPUfor measuring the branch prediction unit
PERF_COUNT_HW_CACHE_NODE(since Linux 3.1)for measuring local memory accesses
and
perf_hw_cache_op_idis one of
PERF_COUNT_HW_CACHE_OP_READfor read accesses
PERF_COUNT_HW_CACHE_OP_WRITEfor write accesses
PERF_COUNT_HW_CACHE_OP_PREFETCHfor prefetch accesses
and
perf_hw_cache_op_result_idis one of
PERF_COUNT_HW_CACHE_RESULT_ACCESSto measure accesses
PERF_COUNT_HW_CACHE_RESULT_MISSto measure misses
If
typeisPERF_TYPE_RAW, then a custom "raw"configvalue is needed. Most CPUs support events that are not covered by the "generalized" events. These are implementation defined; see your CPU manual (for example the Intel Volume 3B documentation or the AMD BIOS and Kernel Developer Guide). The libpfm4 library can be used to translate from the name in the architectural manuals to the raw hex valueperf_event_open() expects in this field.If
typeisPERF_TYPE_BREAKPOINT, then leaveconfigset to zero. Its parameters are set in other places.
sample_period,
sample_freqA "sampling" event is one that generates an
overflow notification every N events, where N is
given by sample_period. A
sampling event has sample_period > 0.
When an overflow occurs, requested data is recorded
in the mmap buffer. The sample_type field
controls what data is recorded on each overflow.
sample_freq can be
used if you wish to use frequency rather than period.
In this case, you set the freq flag. The kernel
will adjust the sampling period to try and achieve
the desired rate. The rate of adjustment is a timer
tick.
sample_typeThe various bits in this field specify which values to include in the sample. They will be recorded in a ring-buffer, which is available to user space using mmap(2). The order in which the values are saved in the sample are documented in the MMAP Layout subsection below; it is not the enum perf_event_sample_format order.
PERF_SAMPLE_IPRecords instruction pointer.
PERF_SAMPLE_TIDRecords the process and thread IDs.
PERF_SAMPLE_TIMERecords a timestamp.
PERF_SAMPLE_ADDRRecords an address, if applicable.
PERF_SAMPLE_READRecord counter values for all events in a group, not just the group leader.
PERF_SAMPLE_CALLCHAINRecords the callchain (stack backtrace).
PERF_SAMPLE_IDRecords a unique ID for the opened event's group leader.
PERF_SAMPLE_CPURecords CPU number.
PERF_SAMPLE_PERIODRecords the current sampling period.
PERF_SAMPLE_STREAM_IDRecords a unique ID for the opened event. Unlike
PERF_SAMPLE_IDthe actual ID is returned, not the group leader. This ID is the same as the one returned byPERF_FORMAT_ID.PERF_SAMPLE_RAWRecords additional data, if applicable. Usually returned by tracepoint events.
PERF_SAMPLE_BRANCH_STACK(since Linux 3.4)This provides a record of recent branches, as provided by CPU branch sampling hardware (such as Intel Last Branch Record). Not all hardware supports this feature.
See the
branch_sample_typefield for how to filter which branches are reported.PERF_SAMPLE_REGS_USER(since Linux 3.7)Records the current user-level CPU register state (the values in the process before the kernel was called).
PERF_SAMPLE_STACK_USER(since Linux 3.7)Records the user level stack, allowing stack unwinding.
PERF_SAMPLE_WEIGHT(since Linux 3.10)Records a hardware provided weight value that expresses how costly the sampled event was. This allows the hardware to highlight expensive events in a profile.
PERF_SAMPLE_DATA_SRC(since Linux 3.10)Records the data source: where in the memory hierarchy the data associated with the sampled instruction came from. This is available only if the underlying hardware supports this feature.
PERF_SAMPLE_IDENTIFIER(since Linux 3.12)Places the
SAMPLE_IDvalue in a fixed position in the record, either at the beginning (for sample events) or at the end (if a non-sample event).This was necessary because a sample stream may have records from various different event sources with different
sample_typesettings. Parsing the event stream properly was not possible because the format of the record was needed to findSAMPLE_ID, but the format could not be found without knowing what event the sample belonged to (causing a circular dependency).The
PERF_SAMPLE_IDENTIFIERsetting makes the event stream always parsable by puttingSAMPLE_IDin a fixed location, even though it means having duplicateSAMPLE_IDvalues in records.PERF_SAMPLE_TRANSACTION(since Linux 3.13)Records reasons for transactional memory abort events (for example, from Intel TSX transactional memory support).
The
precise_ipsetting must be greater than 0 and a transactional memory abort event must be measured or no values will be recorded. Also note that some perf_event measurements, such as sampled cycle counting, may cause extraneous aborts (by causing an interrupt during a transaction).PERF_SAMPLE_REGS_INTR(since Linux 3.19)Records a subset of the current CPU register state as specified by
sample_regs_intr. UnlikePERF_SAMPLE_REGS_USERthe register values will return kernel register state if the overflow happened while kernel code is running. If the CPU supports hardware sampling of register state (i.e. PEBS on Intel x86) andprecise_ipis set higher than zero then the register values returned are those captured by hardware at the time of the sampled instruction's retirement.
read_formatThis field specifies the format of the data
returned by read(2) on a
perf_event_open() file
descriptor.
PERF_FORMAT_TOTAL_TIME_ENABLEDAdds the 64-bit
time_enabledfield. This can be used to calculate estimated totals if the PMU is overcommitted and multiplexing is happening.PERF_FORMAT_TOTAL_TIME_RUNNINGAdds the 64-bit
time_runningfield. This can be used to calculate estimated totals if the PMU is overcommitted and multiplexing is happening.PERF_FORMAT_IDAdds a 64-bit unique value that corresponds to the event group.
PERF_FORMAT_GROUPAllows all counter values in an event group to be read with one read.
disabledThe disabled bit
specifies whether the counter starts out disabled or
enabled. If disabled, the event can later be enabled
by ioctl(2), prctl(2), or
enable_on_exec.
When creating an event group, typically the group
leader is initialized with disabled set to 1 and
any child events are initialized with disabled set to 0.
Despite disabled being 0, the
child events will not start until the group leader is
enabled.
inheritThe inherit bit specifies
that this counter should count events of child tasks
as well as the task specified. This applies only to
new children, not to any existing children at the
time the counter is created (nor to any new children
of existing children).
Inherit does not work for some combinations of
read_formats, such as
PERF_FORMAT_GROUP.
pinnedThe pinned bit specifies
that the counter should always be on the CPU if at
all possible. It applies only to hardware counters
and only to group leaders. If a pinned counter cannot
be put onto the CPU (e.g., because there are not
enough hardware counters or because of a conflict
with some other event), then the counter goes into an
'error' state, where reads return end-of-file (i.e.,
read(2) returns 0)
until the counter is subsequently enabled or
disabled.
exclusiveThe exclusive bit
specifies that when this counter's group is on the
CPU, it should be the only group using the CPU's
counters. In the future this may allow monitoring
programs to support PMU features that need to run
alone so that they do not disrupt other hardware
counters.
Note that many unexpected situations may prevent
events with the exclusive bit set
from ever running. This includes any users running a
system-wide measurement as well as any kernel use of
the performance counters (including the commonly
enabled NMI Watchdog Timer interface).
exclude_userIf this bit is set, the count excludes events that happen in user space.
exclude_kernelIf this bit is set, the count excludes events that happen in kernel-space.
exclude_hvIf this bit is set, the count excludes events that happen in the hypervisor. This is mainly for PMUs that have built-in support for handling this (such as POWER). Extra support is needed for handling hypervisor measurements on most machines.
exclude_idleIf set, don't count when the CPU is idle.
mmapThe mmap
bit enables generation of PERF_RECORD_MMAP samples for every
mmap(2) call that
has PROT_EXEC set. This
allows tools to notice new executable code being
mapped into a program (dynamic shared libraries for
example) so that addresses can be mapped back to the
original code.
commThe comm
bit enables tracking of process command name as
modified by the exec(2) and
prctl(PR_SET_NAME)
system calls as well as writing to /proc/self/comm. If the comm_exec flag is
also successfully set (possible since Linux 3.16),
then the misc flag PERF_RECORD_MISC_COMM_EXEC can be
used to differentiate the exec(2) case from the
others.
freqIf this bit is set, then sample_frequency not
sample_period is used
when setting up the sampling interval.
inherit_statThis bit enables saving of event counts on context
switch for inherited tasks. This is meaningful only
if the inherit field is
set.
enable_on_execIf this bit is set, a counter is automatically enabled after a call to exec(2).
taskIf this bit is set, then fork/exit notifications are included in the ring buffer.
watermarkIf set, have an overflow notification happen when
we cross the wakeup_watermark
boundary. Otherwise, overflow notifications happen
after wakeup_events
samples.
precise_ip (since Linux
2.6.35)This controls the amount of skid. Skid is how many instructions execute between an event of interest happening and the kernel being able to stop and record the event. Smaller skid is better and allows more accurate reporting of which events correspond to which instructions, but hardware is often limited with how small this can be.
The values of this are the following:
- 0 -
SAMPLE_IPcan have arbitrary skid.- 1 -
SAMPLE_IPmust have constant skid.- 2 -
SAMPLE_IPrequested to have 0 skid.- 3 -
SAMPLE_IPmust have 0 skid. See alsoPERF_RECORD_MISC_EXACT_IP.
mmap_data (since Linux
2.6.36)The counterpart of the mmap field. This
enables generation of PERF_RECORD_MMAP samples for
mmap(2) calls that
do not have PROT_EXEC
set (for example data and SysV shared memory).
sample_id_all (since
Linux 2.6.38)If set, then TID, TIME, ID, STREAM_ID, and CPU can
additionally be included in non-PERF_RECORD_SAMPLEs if the
corresponding sample_type is
selected.
If PERF_SAMPLE_IDENTIFIER is
specified, then an additional ID value is included as
the last value to ease parsing the record stream.
This may lead to the id value appearing
twice.
The layout is described by this pseudo-structure:
struct sample_id { { u32 pid, tid; } /* if PERF_SAMPLE_TID set */ { u64 time; } /* if PERF_SAMPLE_TIME set */ { u64 id; } /* if PERF_SAMPLE_ID set */ { u64 stream_id;} /* if PERF_SAMPLE_STREAM_ID set */ { u32 cpu, res; } /* if PERF_SAMPLE_CPU set */ { u64 id; } /* if PERF_SAMPLE_IDENTIFIER set */ };
exclude_host(since Linux 3.2)When conducting measurements that include processes running VM instances (i.e. have executed a
KVM_RUNioctl(2) ) only measure events happening inside a guest instance. This is only meaningful outside the guests; this setting does not change counts gathered inside of a guest. Currently, this functionality is x86 only.exclude_guest(since Linux 3.2)When conducting measurements that include processes running VM instances (i.e. have executed a
KVM_RUNioctl(2) ) do not measure events happening inside guest instances. This is only meaningful outside the guests; this setting does not change counts gathered inside of a guest. Currently, this functionality is x86 only.exclude_callchain_kernel(since Linux 3.7)Do not include kernel callchains.
exclude_callchain_user(since Linux 3.7)Do not include user callchains.
mmap2(since Linux 3.16)Generate an extended executable mmap record that contains enough additional information to uniquely identify shared mappings. The
mmapflag must also be set for this to work.comm_exec(since Linux 3.16)This is purely a feature-detection flag, it does not change kernel behavior. If this flag can successfully be set, then, when
commis enabled, thePERF_RECORD_MISC_COMM_EXECflag will be set in themiscfield of a comm record header if the rename event being reported was caused by a call to exec(2). This allows tools to distinguish between the various types of process renaming.use_clockid(since Linux 4.1)This allows selecting which internal Linux clock to use when generating timestamps via the
clockidfield. This can make it easier to correlate perf sample times with timestamps generated by other tools.wakeup_events,wakeup_watermarkThis union sets how many samples (
wakeup_events) or bytes (wakeup_watermark) happen before an overflow notification happens. Which one is used is selected by thewatermarkbit flag.
wakeup_eventscounts onlyPERF_RECORD_SAMPLErecord types. To receive overflow notification for allPERF_RECORDtypes choose watermark and setwakeup_watermarkto 1.Prior to Linux 3.0 setting
wakeup_eventsto 0 resulted in no overflow notifications; more recent kernels treat 0 the same as 1.bp_type(since Linux 2.6.33)This chooses the breakpoint type. It is one of:
HW_BREAKPOINT_EMPTYNo breakpoint.
HW_BREAKPOINT_RCount when we read the memory location.
HW_BREAKPOINT_WCount when we write the memory location.
HW_BREAKPOINT_RWCount when we read or write the memory location.
HW_BREAKPOINT_XCount when we execute code at the memory location.
The values can be combined via a bitwise or, but the combination of
HW_BREAKPOINT_RorHW_BREAKPOINT_WwithHW_BREAKPOINT_Xis not allowed.bp_addr(since Linux 2.6.33)
bp_addraddress of the breakpoint. For execution breakpoints this is the memory address of the instruction of interest; for read and write breakpoints it is the memory address of the memory location of interest.config1(since Linux 2.6.39)
config1is used for setting events that need an extra register or otherwise do not fit in the regular config field. Raw OFFCORE_EVENTS on Nehalem/Westmere/SandyBridge use this field on 3.3 and later kernels.bp_len(since Linux 2.6.33)
bp_lenis the length of the breakpoint being measured iftypeisPERF_TYPE_BREAKPOINT. Options areHW_BREAKPOINT_LEN_1,HW_BREAKPOINT_LEN_2,HW_BREAKPOINT_LEN_4,HW_BREAKPOINT_LEN_8. For an execution breakpoint, set this tosizeof(long).config2(since Linux 2.6.39)
config2is a further extension of theconfig1field.branch_sample_type(since Linux 3.4)If
PERF_SAMPLE_BRANCH_STACKis enabled, then this specifies what branches to include in the branch record.The first part of the value is the privilege level, which is a combination of one of the following values. If the user does not set privilege level explicitly, the kernel will use the event's privilege level. Event and branch privilege levels do not have to match.
PERF_SAMPLE_BRANCH_USERBranch target is in user space.
PERF_SAMPLE_BRANCH_KERNELBranch target is in kernel space.
PERF_SAMPLE_BRANCH_HVBranch target is in hypervisor.
PERF_SAMPLE_BRANCH_PLM_ALLA convenience value that is the three preceding values ORed together.
In addition to the privilege value, at least one or more of the following bits must be set.
PERF_SAMPLE_BRANCH_ANYAny branch type.
PERF_SAMPLE_BRANCH_ANY_CALLAny call branch.
PERF_SAMPLE_BRANCH_ANY_RETURNAny return branch.
PERF_SAMPLE_BRANCH_IND_CALLIndirect calls.
PERF_SAMPLE_BRANCH_COND(since Linux 3.16)Conditional branches.
PERF_SAMPLE_BRANCH_ABORT_TX(since Linux 3.11)Transactional memory aborts.
PERF_SAMPLE_BRANCH_IN_TX(since Linux 3.11)Branch in transactional memory transaction.
PERF_SAMPLE_BRANCH_NO_TX(since Linux 3.11)Branch not in transactional memory transaction.
PERF_SAMPLE_BRANCH_CALL_STACK(since Linux 4.1) Branch is part of a hardware-generated call stack. This requires hardware support, currently only found on Intel x86 Haswell or newer.sample_regs_user(since Linux 3.7)This bit mask defines the set of user CPU registers to dump on samples. The layout of the register mask is architecture-specific and described in the kernel header
arch/ARCH/include/uapi/asm/perf_regs.h.sample_stack_user(since Linux 3.7)This defines the size of the user stack to dump if
PERF_SAMPLE_STACK_USERis specified.clockid(since Linux 4.1)If
use_clockidis set, then this field selects which internal Linux timer to use for timestamps. The available timers are defined inlinux/time.h, withCLOCK_MONOTONIC,CLOCK_MONOTONIC_RAW,CLOCK_REALTIME,CLOCK_BOOTTIME, andCLOCK_TAIcurrently supported.aux_watermark(since Linux 4.1)This specifies how much data is required to trigger a
PERF_RECORD_AUXsample.
Once a perf_event_open()
file descriptor has been opened, the values of the events
can be read from the file descriptor. The values that are
there are specified by the read_format field in the
attr structure at
open time.
If you attempt to read into a buffer that is not big enough to hold the data ENOSPC is returned
Here is the layout of the data returned by a read:
If PERF_FORMAT_GROUP
was specified to allow reading all events in a group
at once:
struct read_format { u64 nr; /* The number of events */ u64 time_enabled; /* if PERF_FORMAT_TOTAL_TIME_ENABLED */ u64 time_running; /* if PERF_FORMAT_TOTAL_TIME_RUNNING */ struct { u64 value; /* The value of the event */ u64 id; /* if PERF_FORMAT_ID */ } values[nr]; };
If PERF_FORMAT_GROUP
was not
specified:
struct read_format { u64 value; /* The value of the event */u64 time_enabled; /* if PERF_FORMAT_TOTAL_TIME_ENABLED */u64 time_running; /* if PERF_FORMAT_TOTAL_TIME_RUNNING */u64 id; /* if PERF_FORMAT_ID */};
The values read are as follows:
nrThe number of events in this file descriptor. Only
available if PERF_FORMAT_GROUP was
specified.
time_enabled, time_runningTotal time the event was enabled and running.
Normally these are the same. If more events are
started, then available counter slots on the PMU,
then multiplexing happens and events run only part of
the time. In that case, the time_enabled and
time running
values can be used to scale an estimated value for
the count.
valueAn unsigned 64-bit value containing the counter result.
idA globally unique value for this particular event,
only present if PERF_FORMAT_ID was specified in
read_format.
When using perf_event_open() in sampled mode,
asynchronous events (like counter overflow or PROT_EXEC mmap tracking) are logged into
a ring-buffer. This ring-buffer is created and accessed
through mmap(2).
The mmap size should be 1+2^n pages, where the first page is a metadata page (struct perf_event_mmap_page) that contains various bits of information such as where the ring-buffer head is.
Before kernel 2.6.39, there is a bug that means you must allocate an mmap ring buffer when sampling even if you do not plan to access it.
The structure of the first metadata mmap page is as follows:
struct perf_event_mmap_page { __u32 version; /* version number of this structure */ __u32 compat_version; /* lowest version this is compat with */ __u32 lock; /* seqlock for synchronization */ __u32 index; /* hardware counter identifier */ __s64 offset; /* add to hardware counter value */ __u64 time_enabled; /* time event active */ __u64 time_running; /* time event on CPU */ union { __u64 capabilities; struct { __u64 cap_usr_time / cap_usr_rdpmc / cap_bit0 : 1, cap_bit0_is_deprecated : 1, cap_user_rdpmc : 1, cap_user_time : 1, cap_user_time_zero : 1, }; }; __u16 pmc_width; __u16 time_shift; __u32 time_mult; __u64 time_offset; __u64 __reserved[120]; /* Pad to 1k */ __u64 data_head; /* head in the data section */ __u64 data_tail; /* user-space written tail */ __u64 data_offset; /* where the buffer starts */ __u64 data_size; /* data buffer size */ __u64 aux_head; __u64 aux_tail; __u64 aux_offset; __u64 aux_size; }
The following list describes the fields in the
perf_event_mmap_page
structure in more detail:
versionVersion number of this structure.
compat_versionThe lowest version this is compatible with.
lockA seqlock for synchronization.
indexA unique hardware counter identifier.
offsetWhen using rdpmc for reads this offset value must be added to the one returned by rdpmc to get the current total event count.
time_enabledTime the event was active.
time_runningTime the event was running.
cap_usr_time /
cap_usr_rdpmc
/ cap_bit0
(since Linux 3.4)There was a bug in the definition of cap_usr_time and
cap_usr_rdpmc from
Linux 3.4 until Linux 3.11. Both bits were defined to
point to the same location, so it was impossible to
know if cap_usr_time or
cap_usr_rdpmc were
actually set.
Starting with Linux 3.12, these are renamed to
cap_bit0
and you should use the cap_user_time and
cap_user_rdpmc fields
instead.
cap_bit0_is_deprecated
(since Linux 3.12)If set, this bit indicates that the kernel
supports the properly separated cap_user_time and
cap_user_rdpmc
bits.
If not-set, it indicates an older kernel where
cap_usr_time and
cap_usr_rdpmc map to
the same bit and thus both features should be used
with caution.
cap_user_rdpmc (since
Linux 3.12)If the hardware supports user-space read of performance counters without syscall (this is the "rdpmc" instruction on x86), then the following code can be used to do a read:
u32 seq, time_mult, time_shift, idx, width; u64 count, enabled, running; u64 cyc, time_offset; do { seq = pc−>lock; barrier(); enabled = pc−>time_enabled; running = pc−>time_running; if (pc−>cap_usr_time && enabled != running) { cyc = rdtsc(); time_offset = pc−>time_offset; time_mult = pc−>time_mult; time_shift = pc−>time_shift; } idx = pc−>index; count = pc−>offset; if (pc−>cap_usr_rdpmc && idx) { width = pc−>pmc_width; count += rdpmc(idx − 1); } barrier(); } while (pc−>lock != seq);
cap_user_time (since
Linux 3.12)This bit indicates the hardware has a constant, nonstop timestamp counter (TSC on x86).
cap_user_time_zero
(since Linux 3.12)Indicates the presence of time_zero which
allows mapping timestamp values to the hardware
clock.
pmc_widthIf cap_usr_rdpmc, this
field provides the bit-width of the value read using
the rdpmc or equivalent instruction. This can be used
to sign extend the result like:
pmc <<= 64 − pmc_width; pmc >>= 64 − pmc_width; // signed shift right count += pmc;
time_shift, time_mult, time_offsetIf cap_usr_time, these
fields can be used to compute the time delta since
time_enabled (in nanoseconds) using rdtsc or
similar.
u64 quot, rem;
u64 delta;
quot = (cyc >> time_shift);
rem = cyc & ((1 << time_shift) − 1);
delta = time_offset + quot * time_mult +
((rem * time_mult) >> time_shift);
Where time_offset,
time_mult,
time_shift,
and cyc are
read in the seqcount loop described above. This delta
can then be added to enabled and possible running (if
idx), improving the scaling:
enabled += delta;
if (idx)
running += delta;
quot = count / running;
rem = count % running;
count = quot * enabled + (rem * enabled) / running;
time_zero (since Linux
3.12)If cap_usr_time_zero is
set, then the hardware clock (the TSC timestamp
counter on x86) can be calculated from the time_zero, time_mult, and
time_shift
values:
time = timestamp - time_zero;
quot = time / time_mult;
rem = time % time_mult;
cyc = (quot << time_shift) + (rem << time_shift) / time_mult;
And vice versa:
quot = cyc >> time_shift;
rem = cyc & ((1 << time_shift) - 1);
timestamp = time_zero + quot * time_mult +
((rem * time_mult) >> time_shift);
data_headThis points to the head of the data section. The value continuously increases, it does not wrap. The value needs to be manually wrapped by the size of the mmap buffer before accessing the samples.
On SMP-capable platforms, after reading the
data_head
value, user space should issue an rmb().
data_tailWhen the mapping is PROT_WRITE, the data_tail value
should be written by user space to reflect the last
read data. In this case, the kernel will not
overwrite unread data.
data_offset (since
Linux 4.1)Contains the offset of the location in the mmap buffer where perf sample data begins.
data_size (since Linux
4.1)Contains the size of the perf sample region within the mmap buffer.
aux_head, aux_tail, aux_offset, aux_size (since Linux
4.1)The AUX region allows mmaping a separate sample buffer for high-bandwidth data streams (separate from the main perf sample buffer). An example of a high-bandwidth stream is instruction tracing support, as is found in newer Intel processors.
To set up an AUX area, first aux_offset needs to
be set with an offset greater than data_offset+data_size
and aux_size needs to be
set to the desired buffer size. The desired offset
and size must be page aligned, and the size must be a
power of two. These values are then passed to mmap in
order to map the AUX buffer. Pages in the AUX buffer
are included as part of the RLIMIT_MEMLOCK resource limit (see
setrlimit(2)), and
also as part of the perf_event_mlock_kb
allowance.
By default, the AUX buffer will be truncated if it will not fit in the available space in the ring buffer. If the AUX buffer is mapped as a read only buffer, then it will operate in ring buffer mode where old data will be overwritten by new. In overwrite mode, it might not be possible to infer where the new data began, and it is the consumer's job to disable measurement while reading to avoid possible data races.
The aux_head and
aux_tail
ring buffer pointers have the same behavior and
ordering rules as the previous described data_head and
data_tail.
The following 2^n ring-buffer pages have the layout described below.
If perf_event_attr.sample_id_all
is set, then all event types will have the sample_type
selected fields related to where/when (identity) an event
took place (TID, TIME, ID, CPU, STREAM_ID) described in
PERF_RECORD_SAMPLE below, it
will be stashed just after the perf_event_header and the
fields already present for the existing fields, that is, at
the end of the payload. That way a newer perf.data file
will be supported by older perf tools, with these new
optional fields being ignored.
The mmap values start with a header:
struct perf_event_header { __u32 type;__u16 misc;__u16 size;};
Below, we describe the perf_event_header fields in
more detail. For ease of reading, the fields with shorter
descriptions are presented first.
sizeThis indicates the size of the record.
miscThe misc
field contains additional information about the
sample.
The CPU mode can be determined from this value by
masking with PERF_RECORD_MISC_CPUMODE_MASK and
looking for one of the following (note these are not
bit masks, only one can be set at a time):
PERF_RECORD_MISC_CPUMODE_UNKNOWNUnknown CPU mode.
PERF_RECORD_MISC_KERNELSample happened in the kernel.
PERF_RECORD_MISC_USERSample happened in user code.
PERF_RECORD_MISC_HYPERVISORSample happened in the hypervisor.
PERF_RECORD_MISC_GUEST_KERNEL(since Linux 2.6.35)Sample happened in the guest kernel.
- PERF_RECORD_MISC_GUEST_USER (since Linux 2.6.35)
Sample happened in guest user code.
In addition, one of the following bits can be set:
PERF_RECORD_MISC_MMAP_DATA(since Linux 3.10)This is set when the mapping is not executable; otherwise the mapping is executable.
PERF_RECORD_MISC_COMM_EXEC(since Linux 3.16)This is set for a
PERF_RECORD_COMMrecord on kernels more recent than Linux 3.16 if a process name change was caused by an exec(2) system call. It is an alias forPERF_RECORD_MISC_MMAP_DATAsince the two values would not be set in the same record.PERF_RECORD_MISC_EXACT_IPThis indicates that the content of
PERF_SAMPLE_IPpoints to the actual instruction that triggered the event. See alsoperf_event_attr.precise_ip.PERF_RECORD_MISC_EXT_RESERVED(since Linux 2.6.35)This indicates there is extended data available (currently not used).
typeThe type
value is one of the below. The values in the
corresponding record (that follows the header) depend
on the type
selected as shown.
PERF_RECORD_MMAPThe MMAP events record the
PROT_EXECmappings so that we can correlate user-space IPs to code. They have the following structure:
struct { struct perf_event_header header;u32 pid,tid;u64 addr;u64 len;u64 pgoff;char filename[];};
pidis the process ID.
tidis the thread ID.
addris the address of the allocated memory.
lenis the length of the allocated memory.pgoffis the page offset of the allocated memory.filenameis a string describing the backing of the allocated memory.PERF_RECORD_LOSTThis record indicates when events are lost.
struct { struct perf_event_header header;u64 id;u64 lost;struct sample_id sample_id;};
idis the unique event ID for the samples that were lost.
lostis the number of events that were lost.
PERF_RECORD_COMMThis record indicates a change in the process name.
struct { struct perf_event_header header;u32 pid;u32 tid;char comm[];struct sample_id sample_id;};
pidis the process ID.
tidis the thread ID.
commis a string containing the new name of the process.
PERF_RECORD_EXITThis record indicates a process exit event.
struct { struct perf_event_header header;u32 pid,ppid;u32 tid,ptid;u64 time;struct sample_id sample_id;}; PERF_RECORD_THROTTLE,PERF_RECORD_UNTHROTTLEThis record indicates a throttle/unthrottle event.
struct { struct perf_event_header header;u64 time;u64 id;u64 stream_id;struct sample_id sample_id;}; PERF_RECORD_FORKThis record indicates a fork event.
struct { struct perf_event_header header;u32 pid,ppid;u32 tid,ptid;u64 time;struct sample_id sample_id;}; PERF_RECORD_READThis record indicates a read event.
struct { struct perf_event_header header;u32 pid,tid;struct read_format values;struct sample_id sample_id;}; PERF_RECORD_SAMPLEThis record indicates a sample.
struct { struct perf_event_header header; u64 sample_id; /* if PERF_SAMPLE_IDENTIFIER */ u64 ip; /* if PERF_SAMPLE_IP */ u32 pid, tid; /* if PERF_SAMPLE_TID */ u64 time; /* if PERF_SAMPLE_TIME */ u64 addr; /* if PERF_SAMPLE_ADDR */ u64 id; /* if PERF_SAMPLE_ID */ u64 stream_id; /* if PERF_SAMPLE_STREAM_ID */ u32 cpu, res; /* if PERF_SAMPLE_CPU */ u64 period; /* if PERF_SAMPLE_PERIOD */ struct read_format v; /* if PERF_SAMPLE_READ */ u64 nr; /* if PERF_SAMPLE_CALLCHAIN */ u64 ips[nr]; /* if PERF_SAMPLE_CALLCHAIN */ u32 size; /* if PERF_SAMPLE_RAW */ char data[size]; /* if PERF_SAMPLE_RAW */ u64 bnr; /* if PERF_SAMPLE_BRANCH_STACK */ struct perf_branch_entry lbr[bnr]; /* if PERF_SAMPLE_BRANCH_STACK */ u64 abi; /* if PERF_SAMPLE_REGS_USER */ u64 regs[weight(mask)]; /* if PERF_SAMPLE_REGS_USER */ u64 size; /* if PERF_SAMPLE_STACK_USER */ char data[size]; /* if PERF_SAMPLE_STACK_USER */ u64 dyn_size; /* if PERF_SAMPLE_STACK_USER && size != 0 */ u64 weight; /* if PERF_SAMPLE_WEIGHT */ u64 data_src; /* if PERF_SAMPLE_DATA_SRC */ u64 transaction;/* if PERF_SAMPLE_TRANSACTION */ u64 abi; /* if PERF_SAMPLE_REGS_INTR */ u64 regs[weight(mask)]; /* if PERF_SAMPLE_REGS_INTR */ };
sample_idIf
PERF_SAMPLE_IDENTIFIERis enabled, a 64-bit unique ID is included. This is a duplication of thePERF_SAMPLE_IDidvalue, but included at the beginning of the sample so parsers can easily obtain the value.ipIf
PERF_SAMPLE_IPis enabled, then a 64-bit instruction pointer value is included.pid,tidIf
PERF_SAMPLE_TIDis enabled, then a 32-bit process ID and 32-bit thread ID are included.timeIf
PERF_SAMPLE_TIMEis enabled, then a 64-bit timestamp is included. This is obtained via local_clock() which is a hardware timestamp if available and the jiffies value if not.addrIf
PERF_SAMPLE_ADDRis enabled, then a 64-bit address is included. This is usually the address of a tracepoint, breakpoint, or software event; otherwise the value is 0.idIf
PERF_SAMPLE_IDis enabled, a 64-bit unique ID is included. If the event is a member of an event group, the group leader ID is returned. This ID is the same as the one returned byPERF_FORMAT_ID.stream_idIf
PERF_SAMPLE_STREAM_IDis enabled, a 64-bit unique ID is included. UnlikePERF_SAMPLE_IDthe actual ID is returned, not the group leader. This ID is the same as the one returned byPERF_FORMAT_ID.cpu,resIf
PERF_SAMPLE_CPUis enabled, this is a 32-bit value indicating which CPU was being used, in addition to a reserved (unused) 32-bit value.periodIf
PERF_SAMPLE_PERIODis enabled, a 64-bit value indicating the current sampling period is written.vIf
PERF_SAMPLE_READis enabled, a structure of type read_format is included which has values for all events in the event group. The values included depend on theread_formatvalue used atperf_event_open() time.nr,ips[nr]If
PERF_SAMPLE_CALLCHAINis enabled, then a 64-bit number is included which indicates how many following 64-bit instruction pointers will follow. This is the current callchain.size,data[size]If
PERF_SAMPLE_RAWis enabled, then a 32-bit value indicating size is included followed by an array of 8-bit values of length size. The values are padded with 0 to have 64-bit alignment.This RAW record data is opaque with respect to the ABI. The ABI doesn't make any promises with respect to the stability of its content, it may vary depending on event, hardware, and kernel version.
bnr,lbr[bnr]If
PERF_SAMPLE_BRANCH_STACKis enabled, then a 64-bit value indicating the number of records is included, followed bybnrperf_branch_entrystructures which each include the fields:
fromThis indicates the source instruction (may not be a branch).
toThe branch target.
mispredThe branch target was mispredicted.
predictedThe branch target was predicted.
in_tx(since Linux 3.11)The branch was in a transactional memory transaction.
abort(since Linux 3.11)The branch was in an aborted transactional memory transaction.
The entries are from most to least recent, so the first entry has the most recent branch.
Support for
mispredandpredictedis optional; if not supported, both values will be 0.The type of branches recorded is specified by the
branch_sample_typefield.abi,regs[weight(mask)]If
PERF_SAMPLE_REGS_USERis enabled, then the user CPU registers are recorded.The
abifield is one ofPERF_SAMPLE_REGS_ABI_NONE,PERF_SAMPLE_REGS_ABI_32orPERF_SAMPLE_REGS_ABI_64.The
regsfield is an array of the CPU registers that were specified by thesample_regs_userattr field. The number of values is the number of bits set in thesample_regs_userbit mask.size,data[size],dyn_sizeIf
PERF_SAMPLE_STACK_USERis enabled, then the user stack is recorded. This can be used to generate stack backtraces.sizeis the size requested by the user insample_stack_useror else the maximum record size.datais the stack data (a raw dump of the memory pointed to by the stack pointer at the time of sampling).dyn_sizeis the amount of data actually dumped (can be less thansize). Note thatdyn_sizeis omitted ifsizeis 0.weightIf
PERF_SAMPLE_WEIGHTis enabled, then a 64-bit value provided by the hardware is recorded that indicates how costly the event was. This allows expensive events to stand out more clearly in profiles.data_srcIf
PERF_SAMPLE_DATA_SRCis enabled, then a 64-bit value is recorded that is made up of the following fields:
mem_opType of opcode, a bitwise combination of:
PERF_MEM_OP_NANot available
PERF_MEM_OP_LOADLoad instruction
PERF_MEM_OP_STOREStore instruction
PERF_MEM_OP_PFETCHPrefetch
PERF_MEM_OP_EXECExecutable code
mem_lvlMemory hierarchy level hit or miss, a bitwise combination of the following, shifted left by
PERF_MEM_LVL_SHIFT:
PERF_MEM_LVL_NANot available
PERF_MEM_LVL_HITHit
PERF_MEM_LVL_MISSMiss
PERF_MEM_LVL_L1Level 1 cache
PERF_MEM_LVL_LFBLine fill buffer
PERF_MEM_LVL_L2Level 2 cache
PERF_MEM_LVL_L3Level 3 cache
PERF_MEM_LVL_LOC_RAMLocal DRAM
PERF_MEM_LVL_REM_RAM1Remote DRAM 1 hop
PERF_MEM_LVL_REM_RAM2Remote DRAM 2 hops
PERF_MEM_LVL_REM_CCE1Remote cache 1 hop
PERF_MEM_LVL_REM_CCE2Remote cache 2 hops
PERF_MEM_LVL_IOI/O memory
PERF_MEM_LVL_UNCUncached memory
mem_snoopSnoop mode, a bitwise combination of the following, shifted left by
PERF_MEM_SNOOP_SHIFT:
PERF_MEM_SNOOP_NANot available
PERF_MEM_SNOOP_NONENo snoop
PERF_MEM_SNOOP_HITSnoop hit
PERF_MEM_SNOOP_MISSSnoop miss
PERF_MEM_SNOOP_HITMSnoop hit modified
mem_lockLock instruction, a bitwise combination of the following, shifted left by
PERF_MEM_LOCK_SHIFT:
PERF_MEM_LOCK_NANot available
PERF_MEM_LOCK_LOCKEDLocked transaction
mem_dtlbTLB access hit or miss, a bitwise combination of the following, shifted left by
PERF_MEM_TLB_SHIFT:
PERF_MEM_TLB_NANot available
PERF_MEM_TLB_HITHit
PERF_MEM_TLB_MISSMiss
PERF_MEM_TLB_L1Level 1 TLB
PERF_MEM_TLB_L2Level 2 TLB
PERF_MEM_TLB_WKHardware walker
PERF_MEM_TLB_OSOS fault handler
transactionIf the
PERF_SAMPLE_TRANSACTIONflag is set, then a 64-bit field is recorded describing the sources of any transactional memory aborts.The field is a bitwise combination of the following values:
PERF_TXN_ELISIONAbort from an elision type transaction (Intel-CPU-specific).
PERF_TXN_TRANSACTIONAbort from a generic transaction.
PERF_TXN_SYNCSynchronous abort (related to the reported instruction).
PERF_TXN_ASYNCAsynchronous abort (not related to the reported instruction).
PERF_TXN_RETRYRetryable abort (retrying the transaction may have succeeded).
PERF_TXN_CONFLICTAbort due to memory conflicts with other threads.
PERF_TXN_CAPACITY_WRITEAbort due to write capacity overflow.
PERF_TXN_CAPACITY_READAbort due to read capacity overflow.
In addition, a user-specified abort code can be obtained from the high 32 bits of the field by shifting right by
PERF_TXN_ABORT_SHIFTand masking withPERF_TXN_ABORT_MASK.abi,regs[weight(mask)]If
PERF_SAMPLE_REGS_INTRis enabled, then the user CPU registers are recorded.The
abifield is one ofPERF_SAMPLE_REGS_ABI_NONE,PERF_SAMPLE_REGS_ABI_32orPERF_SAMPLE_REGS_ABI_64.The
regsfield is an array of the CPU registers that were specified by thesample_regs_intrattr field. The number of values is the number of bits set in thesample_regs_intrbit mask.
PERF_RECORD_MMAP2This record includes extended information on mmap(2) calls returning executable mappings. The format is similar to that of the
PERF_RECORD_MMAPrecord, but includes extra values that allow uniquely identifying shared mappings.
struct { struct perf_event_header header;u32 pid;u32 tid;u64 addr;u64 len;u64 pgoff;u32 maj;u32 min;u64 ino;u64 ino_generation;u32 prot;u32 flags;char filename[];struct sample_id sample_id;};
pidis the process ID.
tidis the thread ID.
addris the address of the allocated memory.
lenis the length of the allocated memory.
pgoffis the page offset of the allocated memory.
majis the major ID of the underlying device.
minis the minor ID of the underlying device.
inois the inode number.
ino_generationis the inode generation.
protis the protection information.
flagsis the flags information.
filenameis a string describing the backing of the allocated memory.
PERF_RECORD_AUX(since Linux 4.1)This record reports that new data is available in the separate AUX buffer region.
struct { struct perf_event_header header;u64 aux_offset;u64 aux_size;u64 flags;struct sample_id sample_id;};
aux_offsetoffset in the AUX mmap region where the new data begins.
aux_sizesize of the data made available.
flagsdescribes the AUX update.
PERF_AUX_FLAG_TRUNCATEDif set, then the data returned was truncated to fit the available buffer size.
PERF_AUX_FLAG_OVERWRITEif set, then the data returned has overwritten previous data.
PERF_RECORD_ITRACE_START(since Linux 4.1)This record indicates which process has initiated an instruction trace event, allowing tools to properly correlate the instruction addresses in the AUX buffer with the proper executable.
struct { struct perf_event_header header;u32 pid;u32 tid;};
pidprocess ID of the thread starting an instruction trace.
tidthread ID of the thread starting an instruction trace.
Events can be set to notify when a threshold is crossed, indicating an overflow. Overflow conditions can be captured by monitoring the event file descriptor with poll(2), select(2), or epoll(2). Alternately, a SIGIO signal handler can be created and the event configured with fcntl(2) to generate SIGIO signals.
Overflows are generated only by sampling events
(sample_period
must have a nonzero value).
There are two ways to generate overflow notifications.
The first is to set a wakeup_events or wakeup_watermark value that
will trigger if a certain number of samples or bytes have
been written to the mmap ring buffer. In this case
POLL_IN is indicated.
The other way is by use of the PERF_EVENT_IOC_REFRESH ioctl. This ioctl
adds to a counter that decrements each time the event
overflows. When nonzero, POLL_IN is indicated, but once the
counter reaches 0 POLL_HUP is
indicated and the underlying event is disabled.
Refreshing an event group leader refreshes all siblings and refreshing with a parameter of 0 currently enables infinite refreshes; these behaviors are unsupported and should not be relied on.
Starting with Linux 3.18, POLL_HUP is indicated if the event being
monitored is attached to a different process and that
process exits.
Starting with Linux 3.4 on x86, you can use the
rdpmc instruction
to get low-latency reads without having to enter the
kernel. Note that using rdpmc is not necessarily
faster than other methods for reading event values.
Support for this can be detected with the cap_usr_rdpmc field in the
mmap page; documentation on how to calculate event values
can be found in that section.
Originally, when rdpmc support was enabled, any process
(not just ones with an active perf event) could use the
rdpmc instruction to access the counters. Starting with
Linux 4.0 rdpmc support is only allowed if an event is
currently enabled in a process's context. To restore the
old behavior, write the value 2 to /sys/devices/cpu/rdpmc.
Various ioctls act on perf_event_open() file descriptors:
PERF_EVENT_IOC_ENABLEThis enables the individual event or event group specified by the file descriptor argument.
If the PERF_IOC_FLAG_GROUP bit is set in
the ioctl argument, then all events in a group are
enabled, even if the event specified is not the group
leader (but see BUGS).
PERF_EVENT_IOC_DISABLEThis disables the individual counter or event group specified by the file descriptor argument.
Enabling or disabling the leader of a group enables or disables the entire group; that is, while the group leader is disabled, none of the counters in the group will count. Enabling or disabling a member of a group other than the leader affects only that counter; disabling a non-leader stops that counter from counting but doesn't affect any other counter.
If the PERF_IOC_FLAG_GROUP bit is set in
the ioctl argument, then all events in a group are
disabled, even if the event specified is not the
group leader (but see BUGS).
PERF_EVENT_IOC_REFRESHNon-inherited overflow counters can use this to
enable a counter for a number of overflows specified
by the argument, after which it is disabled.
Subsequent calls of this ioctl add the argument value
to the current count. An overflow notification with
POLL_IN set will happen
on each overflow until the count reaches 0; when that
happens a notification with POLL_HUP set is sent and the event
is disabled. Using an argument of 0 is considered
undefined behavior.
PERF_EVENT_IOC_RESETReset the event count specified by the file
descriptor argument to zero. This resets only the
counts; there is no way to reset the multiplexing
time_enabled
or time_running
values.
If the PERF_IOC_FLAG_GROUP bit is set in
the ioctl argument, then all events in a group are
reset, even if the event specified is not the group
leader (but see BUGS).
PERF_EVENT_IOC_PERIODThis updates the overflow period for the event.
Since Linux 3.7 (on ARM) and Linux 3.14 (all other architectures), the new period takes effect immediately. On older kernels, the new period did not take effect until after the next overflow.
The argument is a pointer to a 64-bit value containing the desired new period.
Prior to Linux 2.6.36 this ioctl always failed due to a bug in the kernel.
PERF_EVENT_IOC_SET_OUTPUTThis tells the kernel to report event notifications to the specified file descriptor rather than the default one. The file descriptors must all be on the same CPU.
The argument specifies the desired file descriptor, or −1 if output should be ignored.
PERF_EVENT_IOC_SET_FILTER (since
Linux 2.6.33)This adds an ftrace filter to this event.
The argument is a pointer to the desired ftrace filter.
PERF_EVENT_IOC_ID (since Linux
3.12)This returns the event ID value for the given event file descriptor.
The argument is a pointer to a 64-bit unsigned integer to hold the result.
PERF_EVENT_IOC_SET_BPF (since Linux
4.1)This allows attaching a Berkeley Packet Filter
(BPF) program to an existing kprobe tracepoint event.
You need CAP_SYS_ADMIN
privileges to use this ioctl.
The argument is a BPF program file descriptor that was created by a previous bpf(2) system call.
A process can enable or disable all the event groups
that are attached to it using the prctl(2) PR_TASK_PERF_EVENTS_ENABLE and
PR_TASK_PERF_EVENTS_DISABLE
operations. This applies to all counters on the calling
process, whether created by this process or by another, and
does not affect any counters that this process has created
on other processes. It enables or disables only the group
leaders, not any other members in the groups.
Files in /proc/sys/kernel/
/proc/sys/kernel/perf_event_paranoidThe
perf_event_paranoidfile can be set to restrict access to the performance counters.
2allow only user-space measurements (default since Linux 4.6).
1allow both kernel and user measurements (default before Linux 4.6).
0allow access to CPU-specific data but not raw tracepoint samples.
- −1
no restrictions.
The existence of the
perf_event_paranoidfile is the official method for determining if a kernel supportsperf_event_open()./proc/sys/kernel/perf_event_max_sample_rateThis sets the maximum sample rate. Setting this too high can allow users to sample at a rate that impacts overall machine performance and potentially lock up the machine. The default value is 100000 (samples per second).
/proc/sys/kernel/perf_event_mlock_kbMaximum number of pages an unprivileged user can mlock(2). The default is 516 (kB).
Files in /sys/bus/event_source/devices/
Since Linux 2.6.34, the kernel supports having multiple PMUs available for monitoring. Information on how to program these PMUs can be found under
/sys/bus/event_source/devices/. Each subdirectory corresponds to a different PMU.
/sys/bus/event_source/devices/*/type(since Linux 2.6.38)This contains an integer that can be used in the
typefield of perf_event_attr to indicate that you wish to use this PMU./sys/bus/event_source/devices/cpu/rdpmc(since Linux 3.4)If this file is 1, then direct user-space access to the performance counter registers is allowed via the rdpmc instruction. This can be disabled by echoing 0 to the file.
As of Linux 4.0 the behavior has changed, so that 1 now means only allow access to processes with active perf events, with 2 indicating the old allow-anyone-access behavior.
/sys/bus/event_source/devices/*/format/(since Linux 3.4)This subdirectory contains information on the architecture-specific subfields available for programming the various
configfields in the perf_event_attr struct.The content of each file is the name of the config field, followed by a colon, followed by a series of integer bit ranges separated by commas. For example, the file
eventmay contain the valueconfig1:1,6-10,44which indicates that event is an attribute that occupies bits 1,6-10, and 44 ofperf_event_attr::config1./sys/bus/event_source/devices/*/events/(since Linux 3.4)This subdirectory contains files with predefined events. The contents are strings describing the event settings expressed in terms of the fields found in the previously mentioned
./format/directory. These are not necessarily complete lists of all events supported by a PMU, but usually a subset of events deemed useful or interesting.The content of each file is a list of attribute names separated by commas. Each entry has an optional value (either hex or decimal). If no value is specified, then it is assumed to be a single-bit field with a value of 1. An example entry may look like this:
event=0x2,inv,ldlat=3./sys/bus/event_source/devices/*/ueventThis file is the standard kernel device interface for injecting hotplug events.
/sys/bus/event_source/devices/*/cpumask(since Linux 3.7)The
cpumaskfile contains a comma-separated list of integers that indicate a representative CPU number for each socket (package) on the motherboard. This is needed when setting up uncore or northbridge events, as those PMUs present socket-wide events.
perf_event_open() returns
the new file descriptor, or −1 if an error occurred (in
which case, errno is set
appropriately).
The errors returned by perf_event_open() can be inconsistent, and
may vary across processor architectures and performance
monitoring units.
Returned if the perf_event_attr size value is too small
(smaller than PERF_ATTR_SIZE_VER0), too big (larger
than the page size), or larger than the kernel supports
and the extra bytes are not zero. When E2BIG is returned, the perf_event_attr size field is overwritten
by the kernel to be the size of the structure it was
expecting.
Returned when the requested event requires
CAP_SYS_ADMIN permissions
(or a more permissive perf_event paranoid setting).
Some common cases where an unprivileged process may
encounter this error: attaching to a process owned by a
different user; monitoring all processes on a given CPU
(i.e., specifying the pid argument as
−1); and not setting exclude_kernel when the
paranoid setting requires it.
Returned if the group_fd file descriptor
is not valid, or, if PERF_FLAG_PID_CGROUP is set, the
cgroup file descriptor in pid is not valid.
Returned if another event already has exclusive access to the PMU.
Returned if the attr pointer points at an
invalid memory address.
Returned if the specified event is invalid. There
are many possible reasons for this. A not-exhaustive
list: sample_freq is higher
than the maximum setting; the cpu to monitor does not
exist; read_format is out of
range; sample_type is out of
range; the flags value is out of
range; exclusive or pinned set and the
event is not a group leader; the event config values are out
of range or set reserved bits; the generic event
selected is not supported; or there is not enough room
to add the selected event.
Each opened event uses one file descriptor. If a large number of events are opened, the per-process limit on the number of open file descriptors will be reached, and no more events can be created.
Returned when the event involves a feature not supported by the current CPU.
Returned if the type setting is not
valid. This error is also returned for some unsupported
generic events.
Prior to Linux 3.3, if there was not enough room for the event, ENOSPC was returned. In Linux 3.3, this was changed to EINVAL. ENOSPC is still returned if you try to add more breakpoint events than supported by the hardware.
Returned if PERF_SAMPLE_STACK_USER is set in
sample_type
and it is not supported by hardware.
Returned if an event requiring a specific hardware feature is requested but there is no hardware support. This includes requesting low-skid events if not supported, branch tracing if it is not available, sampling if no PMU interrupt is available, and branch stacks for software events.
Returned on many (but not all) architectures when an
unsupported exclude_hv, exclude_idle,
exclude_user,
or exclude_kernel setting
is specified.
It can also happen, as with EACCES, when the requested event
requires CAP_SYS_ADMIN
permissions (or a more permissive perf_event paranoid
setting). This includes setting a breakpoint on a
kernel address, and (since Linux 3.13) setting a kernel
function-trace tracepoint.
Returned if attempting to attach to a process that does not exist.
perf_event_open() was
introduced in Linux 2.6.31 but was called perf_counter_open(). It was renamed in
Linux 2.6.32.
This perf_event_open()
system call Linux- specific and should not be used in
programs intended to be portable.
Glibc does not provide a wrapper for this system call; call it using syscall(2). See the example below.
The official way of knowing if perf_event_open() support is enabled is
checking for the existence of the file /proc/sys/kernel/perf_event_paranoid.
The F_SETOWN_EX option to
fcntl(2) is needed to
properly get overflow signals in threads. This was introduced
in Linux 2.6.32.
Prior to Linux 2.6.33 (at least for x86), the kernel did
not check if events could be scheduled together until read
time. The same happens on all known kernels if the NMI
watchdog is enabled. This means to see if a given set of
events works you have to perf_event_open(), start, then read before
you know for sure you can get valid measurements.
Prior to Linux 2.6.34, event constraints were not enforced by the kernel. In that case, some events would silently return "0" if the kernel scheduled them in an improper counter slot.
Prior to Linux 2.6.34, there was a bug when multiplexing where the wrong results could be returned.
Kernels from Linux 2.6.35 to Linux 2.6.39 can quickly crash the kernel if "inherit" is enabled and many threads are started.
Prior to Linux 2.6.35, PERF_FORMAT_GROUP did not work with
attached processes.
There is a bug in the kernel code between Linux 2.6.36 and Linux 3.0 that ignores the "watermark" field and acts as if a wakeup_event was chosen if the union has a nonzero value in it.
From Linux 2.6.31 to Linux 3.4, the PERF_IOC_FLAG_GROUP ioctl argument was
broken and would repeatedly operate on the event specified
rather than iterating across all sibling events in a
group.
From Linux 3.4 to Linux 3.11, the mmap cap_usr_rdpmc and cap_usr_time bits mapped to
the same location. Code should migrate to the new cap_user_rdpmc and cap_user_time fields
instead.
Always double-check your results! Various generalized events have had wrong values. For example, retired branches measured the wrong thing on AMD machines until Linux 2.6.35.
The following is a short example that measures the total instruction count of a call to printf(3).
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <sys/ioctl.h>
#include <linux/perf_event.h>
#include <asm/unistd.h>
static long
perf_event_open(struct perf_event_attr *hw_event, pid_t pid,
int cpu, int group_fd, unsigned long flags)
{
int ret;
ret = syscall(__NR_perf_event_open, hw_event, pid, cpu,
group_fd, flags);
return ret;
}
int
main(int argc, char **argv)
{
struct perf_event_attr pe;
long long count;
int fd;
memset(&pe, 0, sizeof(struct perf_event_attr));
pe.type = PERF_TYPE_HARDWARE;
pe.size = sizeof(struct perf_event_attr);
pe.config = PERF_COUNT_HW_INSTRUCTIONS;
pe.disabled = 1;
pe.exclude_kernel = 1;
pe.exclude_hv = 1;
fd = perf_event_open(&pe, 0, −1, −1, 0);
if (fd == −1) {
fprintf(stderr, "Error opening leader %llx\n", pe.config);
exit(EXIT_FAILURE);
}
ioctl(fd, PERF_EVENT_IOC_RESET, 0);
ioctl(fd, PERF_EVENT_IOC_ENABLE, 0);
printf("Measuring instruction count for this printf\n");
ioctl(fd, PERF_EVENT_IOC_DISABLE, 0);
read(fd, &count, sizeof(long long));
printf("Used %lld instructions\n", count);
close(fd);
}
This page is part of release 4.07 of the Linux man-pages project. A
description of the project, information about reporting bugs,
and the latest version of this page, can be found at
https://www.kernel.org/doc/man−pages/.
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Copyright (c) 2012, Vincent Weaver %%%LICENSE_START(GPLv2+_DOC_FULL) This is free documentation; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. The GNU General Public License's references to "object code" and "executables" are to be interpreted as the output of any document formatting or typesetting system, including intermediate and printed output. This manual is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this manual; if not, see <http://www.gnu.org/licenses/>. %%%LICENSE_END This document is based on the perf_event.h header file, the tools/perf/design.txt file, and a lot of bitter experience. |