tools/perf/Documentation/perf-record.txt

perf-record(1)
==============

NAME
----
perf-record - Run a command and record its profile into perf.data

SYNOPSIS
--------
[verse]
'perf record' [-e <EVENT> | --event=EVENT] [-a] <command>
'perf record' [-e <EVENT> | --event=EVENT] [-a] \-- <command> [<options>]

DESCRIPTION
-----------
This command runs a command and gathers a performance counter profile
from it, into perf.data - without displaying anything.

This file can then be inspected later on, using 'perf report'.


OPTIONS
-------
<command>...::
	Any command you can specify in a shell.

-e::
--event=::
	Select the PMU event. Selection can be:

        - a symbolic event name	(use 'perf list' to list all events)

        - a raw PMU event in the form of rN where N is a hexadecimal value
          that represents the raw register encoding with the layout of the
          event control registers as described by entries in
          /sys/bus/event_source/devices/cpu/format/*.

        - a symbolic or raw PMU event followed by an optional colon
	  and a list of event modifiers, e.g., cpu-cycles:p.  See the
	  linkperf:perf-list[1] man page for details on event modifiers.

	- a symbolically formed PMU event like 'pmu/param1=0x3,param2/' where
	  'param1', 'param2', etc are defined as formats for the PMU in
	  /sys/bus/event_source/devices/<pmu>/format/*.

	- a symbolically formed event like 'pmu/config=M,config1=N,config3=K/'

          where M, N, K are numbers (in decimal, hex, octal format). Acceptable
          values for each of 'config', 'config1' and 'config2' are defined by
          corresponding entries in /sys/bus/event_source/devices/<pmu>/format/*
          param1 and param2 are defined as formats for the PMU in:
          /sys/bus/event_source/devices/<pmu>/format/*

	  There are also some parameters which are not defined in .../<pmu>/format/*.
	  These params can be used to overload default config values per event.
	  Here are some common parameters:
	  - 'period': Set event sampling period
	  - 'freq': Set event sampling frequency
	  - 'time': Disable/enable time stamping. Acceptable values are 1 for
		    enabling time stamping. 0 for disabling time stamping.
		    The default is 1.
	  - 'call-graph': Disable/enable callgraph. Acceptable str are "fp" for
			 FP mode, "dwarf" for DWARF mode, "lbr" for LBR mode and
			 "no" for disable callgraph.
	  - 'stack-size': user stack size for dwarf mode
	  - 'name' : User defined event name. Single quotes (') may be used to
		    escape symbols in the name from parsing by shell and tool
		    like this: name=\'CPU_CLK_UNHALTED.THREAD:cmask=0x1\'.
	  - 'aux-output': Generate AUX records instead of events. This requires
			  that an AUX area event is also provided.
	  - 'aux-sample-size': Set sample size for AUX area sampling. If the
	  '--aux-sample' option has been used, set aux-sample-size=0 to disable
	  AUX area sampling for the event.

          See the linkperf:perf-list[1] man page for more parameters.

	  Note: If user explicitly sets options which conflict with the params,
	  the value set by the parameters will be overridden.

	  Also not defined in .../<pmu>/format/* are PMU driver specific
	  configuration parameters.  Any configuration parameter preceded by
	  the letter '@' is not interpreted in user space and sent down directly
	  to the PMU driver.  For example:

	  perf record -e some_event/@cfg1,@cfg2=config/ ...

	  will see 'cfg1' and 'cfg2=config' pushed to the PMU driver associated
	  with the event for further processing.  There is no restriction on
	  what the configuration parameters are, as long as their semantic is
	  understood and supported by the PMU driver.

        - a hardware breakpoint event in the form of '\mem:addr[/len][:access]'
          where addr is the address in memory you want to break in.
          Access is the memory access type (read, write, execute) it can
          be passed as follows: '\mem:addr[:[r][w][x]]'. len is the range,
          number of bytes from specified addr, which the breakpoint will cover.
          If you want to profile read-write accesses in 0x1000, just set
          'mem:0x1000:rw'.
          If you want to profile write accesses in [0x1000~1008), just set
          'mem:0x1000/8:w'.

        - a BPF source file (ending in .c) or a precompiled object file (ending
          in .o) selects one or more BPF events.
          The BPF program can attach to various perf events based on the ELF section
          names.

          When processing a '.c' file, perf searches an installed LLVM to compile it
          into an object file first. Optional clang options can be passed via the
          '--clang-opt' command line option, e.g.:

            perf record --clang-opt "-DLINUX_VERSION_CODE=0x50000" \
                        -e tests/bpf-script-example.c

          Note: '--clang-opt' must be placed before '--event/-e'.

	- a group of events surrounded by a pair of brace ("{event1,event2,...}").
	  Each event is separated by commas and the group should be quoted to
	  prevent the shell interpretation.  You also need to use --group on
	  "perf report" to view group events together.

--filter=<filter>::
	Event filter.  This option should follow an event selector (-e).
	If the event is a tracepoint, the filter string will be parsed by
	the kernel.  If the event is a hardware trace PMU (e.g. Intel PT
	or CoreSight), it'll be processed as an address filter.  Otherwise
	it means a general filter using BPF which can be applied for any
	kind of event.

	- tracepoint filters

	In the case of tracepoints, multiple '--filter' options are combined
	using '&&'.

	- address filters

	A hardware trace PMU advertises its ability to accept a number of
	address filters	by specifying a non-zero value in
	/sys/bus/event_source/devices/<pmu>/nr_addr_filters.

	Address filters have the format:

	filter|start|stop|tracestop <start> [/ <size>] [@<file name>]

	Where:
	- 'filter': defines a region that will be traced.
	- 'start': defines an address at which tracing will begin.
	- 'stop': defines an address at which tracing will stop.
	- 'tracestop': defines a region in which tracing will stop.

	<file name> is the name of the object file, <start> is the offset to the
	code to trace in that file, and <size> is the size of the region to
	trace. 'start' and 'stop' filters need not specify a <size>.

	If no object file is specified then the kernel is assumed, in which case
	the start address must be a current kernel memory address.

	<start> can also be specified by providing the name of a symbol. If the
	symbol name is not unique, it can be disambiguated by inserting #n where
	'n' selects the n'th symbol in address order. Alternately #0, #g or #G
	select only a global symbol. <size> can also be specified by providing
	the name of a symbol, in which case the size is calculated to the end
	of that symbol. For 'filter' and 'tracestop' filters, if <size> is
	omitted and <start> is a symbol, then the size is calculated to the end
	of that symbol.

	If <size> is omitted and <start> is '*', then the start and size will
	be calculated from the first and last symbols, i.e. to trace the whole
	file.

	If symbol names (or '*') are provided, they must be surrounded by white
	space.

	The filter passed to the kernel is not necessarily the same as entered.
	To see the filter that is passed, use the -v option.

	The kernel may not be able to configure a trace region if it is not
	within a single mapping.  MMAP events (or /proc/<pid>/maps) can be
	examined to determine if that is a possibility.

	Multiple filters can be separated with space or comma.

	- bpf filters

	A BPF filter can access the sample data and make a decision based on the
	data.  Users need to set an appropriate sample type to use the BPF
	filter.  BPF filters need root privilege.

	The sample data field can be specified in lower case letter.  Multiple
	filters can be separated with comma.  For example,

	  --filter 'period > 1000, cpu == 1'
	or
	  --filter 'mem_op == load || mem_op == store, mem_lvl > l1'

	The former filter only accept samples with period greater than 1000 AND
	CPU number is 1.  The latter one accepts either load and store memory
	operations but it should have memory level above the L1.  Since the
	mem_op and mem_lvl fields come from the (memory) data_source, it'd only
	work with some events which set the data_source field.

	Also user should request to collect that information (with -d option in
	the above case).  Otherwise, the following message will be shown.

	  $ sudo perf record -e cycles --filter 'mem_op == load'
	  Error: cycles event does not have PERF_SAMPLE_DATA_SRC
	   Hint: please add -d option to perf record.
	  failed to set filter "BPF" on event cycles with 22 (Invalid argument)

	Essentially the BPF filter expression is:

	  <term> <operator> <value> (("," | "||") <term> <operator> <value>)*

	The <term> can be one of:
	  ip, id, tid, pid, cpu, time, addr, period, txn, weight, phys_addr,
	  code_pgsz, data_pgsz, weight1, weight2, weight3, ins_lat, retire_lat,
	  p_stage_cyc, mem_op, mem_lvl, mem_snoop, mem_remote, mem_lock,
	  mem_dtlb, mem_blk, mem_hops

	The <operator> can be one of:
	  ==, !=, >, >=, <, <=, &

	The <value> can be one of:
	  <number> (for any term)
	  na, load, store, pfetch, exec (for mem_op)
	  l1, l2, l3, l4, cxl, io, any_cache, lfb, ram, pmem (for mem_lvl)
	  na, none, hit, miss, hitm, fwd, peer (for mem_snoop)
	  remote (for mem_remote)
	  na, locked (for mem_locked)
	  na, l1_hit, l1_miss, l2_hit, l2_miss, any_hit, any_miss, walk, fault (for mem_dtlb)
	  na, by_data, by_addr (for mem_blk)
	  hops0, hops1, hops2, hops3 (for mem_hops)

--exclude-perf::
	Don't record events issued by perf itself. This option should follow
	an event selector (-e) which selects tracepoint event(s). It adds a
	filter expression 'common_pid != $PERFPID' to filters. If other
	'--filter' exists, the new filter expression will be combined with
	them by '&&'.

-a::
--all-cpus::
        System-wide collection from all CPUs (default if no target is specified).

-p::
--pid=::
	Record events on existing process ID (comma separated list).

-t::
--tid=::
        Record events on existing thread ID (comma separated list).
        This option also disables inheritance by default.  Enable it by adding
        --inherit.

-u::
--uid=::
        Record events in threads owned by uid. Name or number.

-r::
--realtime=::
	Collect data with this RT SCHED_FIFO priority.

--no-buffering::
	Collect data without buffering.

-c::
--count=::
	Event period to sample.

-o::
--output=::
	Output file name.

-i::
--no-inherit::
	Child tasks do not inherit counters.

-F::
--freq=::
	Profile at this frequency. Use 'max' to use the currently maximum
	allowed frequency, i.e. the value in the kernel.perf_event_max_sample_rate
	sysctl. Will throttle down to the currently maximum allowed frequency.
	See --strict-freq.

--strict-freq::
	Fail if the specified frequency can't be used.

-m::
--mmap-pages=::
	Number of mmap data pages (must be a power of two) or size
	specification with appended unit character - B/K/M/G. The
	size is rounded up to have nearest pages power of two value.
	Also, by adding a comma, the number of mmap pages for AUX
	area tracing can be specified.

-g::
	Enables call-graph (stack chain/backtrace) recording for both
	kernel space and user space.

--call-graph::
	Setup and enable call-graph (stack chain/backtrace) recording,
	implies -g.  Default is "fp" (for user space).

	The unwinding method used for kernel space is dependent on the
	unwinder used by the active kernel configuration, i.e
	CONFIG_UNWINDER_FRAME_POINTER (fp) or CONFIG_UNWINDER_ORC (orc)

	Any option specified here controls the method used for user space.

	Valid options are "fp" (frame pointer), "dwarf" (DWARF's CFI -
	Call Frame Information) or "lbr" (Hardware Last Branch Record
	facility).

	In some systems, where binaries are build with gcc
	--fomit-frame-pointer, using the "fp" method will produce bogus
	call graphs, using "dwarf", if available (perf tools linked to
	the libunwind or libdw library) should be used instead.
	Using the "lbr" method doesn't require any compiler options. It
	will produce call graphs from the hardware LBR registers. The
	main limitation is that it is only available on new Intel
	platforms, such as Haswell. It can only get user call chain. It
	doesn't work with branch stack sampling at the same time.

	When "dwarf" recording is used, perf also records (user) stack dump
	when sampled.  Default size of the stack dump is 8192 (bytes).
	User can change the size by passing the size after comma like
	"--call-graph dwarf,4096".

	When "fp" recording is used, perf tries to save stack enties
	up to the number specified in sysctl.kernel.perf_event_max_stack
	by default.  User can change the number by passing it after comma
	like "--call-graph fp,32".

-q::
--quiet::
	Don't print any warnings or messages, useful for scripting.

-v::
--verbose::
	Be more verbose (show counter open errors, etc).

-s::
--stat::
	Record per-thread event counts.  Use it with 'perf report -T' to see
	the values.

-d::
--data::
	Record the sample virtual addresses.

--phys-data::
	Record the sample physical addresses.

--data-page-size::
	Record the sampled data address data page size.

--code-page-size::
	Record the sampled code address (ip) page size

-T::
--timestamp::
	Record the sample timestamps. Use it with 'perf report -D' to see the
	timestamps, for instance.

-P::
--period::
	Record the sample period.

--sample-cpu::
	Record the sample cpu.

--sample-identifier::
	Record the sample identifier i.e. PERF_SAMPLE_IDENTIFIER bit set in
	the sample_type member of the struct perf_event_attr argument to the
	perf_event_open system call.

-n::
--no-samples::
	Don't sample.

-R::
--raw-samples::
Collect raw sample records from all opened counters (default for tracepoint counters).

-C::
--cpu::
Collect samples only on the list of CPUs provided. Multiple CPUs can be provided as a
comma-separated list with no space: 0,1. Ranges of CPUs are specified with -: 0-2.
In per-thread mode with inheritance mode on (default), samples are captured only when
the thread executes on the designated CPUs. Default is to monitor all CPUs.

-B::
--no-buildid::
Do not save the build ids of binaries in the perf.data files. This skips
post processing after recording, which sometimes makes the final step in
the recording process to take a long time, as it needs to process all
events looking for mmap records. The downside is that it can misresolve
symbols if the workload binaries used when recording get locally rebuilt
or upgraded, because the only key available in this case is the
pathname. You can also set the "record.build-id" config variable to
'skip to have this behaviour permanently.

-N::
--no-buildid-cache::
Do not update the buildid cache. This saves some overhead in situations
where the information in the perf.data file (which includes buildids)
is sufficient.  You can also set the "record.build-id" config variable to
'no-cache' to have the same effect.

-G name,...::
--cgroup name,...::
monitor only in the container (cgroup) called "name". This option is available only
in per-cpu mode. The cgroup filesystem must be mounted. All threads belonging to
container "name" are monitored when they run on the monitored CPUs. Multiple cgroups
can be provided. Each cgroup is applied to the corresponding event, i.e., first cgroup
to first event, second cgroup to second event and so on. It is possible to provide
an empty cgroup (monitor all the time) using, e.g., -G foo,,bar. Cgroups must have
corresponding events, i.e., they always refer to events defined earlier on the command
line. If the user wants to track multiple events for a specific cgroup, the user can
use '-e e1 -e e2 -G foo,foo' or just use '-e e1 -e e2 -G foo'.

If wanting to monitor, say, 'cycles' for a cgroup and also for system wide, this
command line can be used: 'perf stat -e cycles -G cgroup_name -a -e cycles'.

-b::
--branch-any::
Enable taken branch stack sampling. Any type of taken branch may be sampled.
This is a shortcut for --branch-filter any. See --branch-filter for more infos.

-j::
--branch-filter::
Enable taken branch stack sampling. Each sample captures a series of consecutive
taken branches. The number of branches captured with each sample depends on the
underlying hardware, the type of branches of interest, and the executed code.
It is possible to select the types of branches captured by enabling filters. The
following filters are defined:

        - any:  any type of branches
        - any_call: any function call or system call
        - any_ret: any function return or system call return
        - ind_call: any indirect branch
        - ind_jmp: any indirect jump
        - call: direct calls, including far (to/from kernel) calls
        - u:  only when the branch target is at the user level
        - k: only when the branch target is in the kernel
        - hv: only when the target is at the hypervisor level
	- in_tx: only when the target is in a hardware transaction
	- no_tx: only when the target is not in a hardware transaction
	- abort_tx: only when the target is a hardware transaction abort
	- cond: conditional branches
	- call_stack: save call stack
	- no_flags: don't save branch flags e.g prediction, misprediction etc
	- no_cycles: don't save branch cycles
	- hw_index: save branch hardware index
	- save_type: save branch type during sampling in case binary is not available later
		     For the platforms with Intel Arch LBR support (12th-Gen+ client or
		     4th-Gen Xeon+ server), the save branch type is unconditionally enabled
		     when the taken branch stack sampling is enabled.
	- priv: save privilege state during sampling in case binary is not available later

+
The option requires at least one branch type among any, any_call, any_ret, ind_call, cond.
The privilege levels may be omitted, in which case, the privilege levels of the associated
event are applied to the branch filter. Both kernel (k) and hypervisor (hv) privilege
levels are subject to permissions.  When sampling on multiple events, branch stack sampling
is enabled for all the sampling events. The sampled branch type is the same for all events.
The various filters must be specified as a comma separated list: --branch-filter any_ret,u,k
Note that this feature may not be available on all processors.

-W::
--weight::
Enable weightened sampling. An additional weight is recorded per sample and can be
displayed with the weight and local_weight sort keys.  This currently works for TSX
abort events and some memory events in precise mode on modern Intel CPUs.

--namespaces::
Record events of type PERF_RECORD_NAMESPACES.  This enables 'cgroup_id' sort key.

--all-cgroups::
Record events of type PERF_RECORD_CGROUP.  This enables 'cgroup' sort key.

--transaction::
Record transaction flags for transaction related events.

--per-thread::
Use per-thread mmaps.  By default per-cpu mmaps are created.  This option
overrides that and uses per-thread mmaps.  A side-effect of that is that
inheritance is automatically disabled.  --per-thread is ignored with a warning
if combined with -a or -C options.

-D::
--delay=::
After starting the program, wait msecs before measuring (-1: start with events
disabled), or enable events only for specified ranges of msecs (e.g.
-D 10-20,30-40 means wait 10 msecs, enable for 10 msecs, wait 10 msecs, enable
for 10 msecs, then stop). Note, delaying enabling of events is useful to filter
out the startup phase of the program, which is often very different.

-I::
--intr-regs::
Capture machine state (registers) at interrupt, i.e., on counter overflows for
each sample. List of captured registers depends on the architecture. This option
is off by default. It is possible to select the registers to sample using their
symbolic names, e.g. on x86, ax, si. To list the available registers use
--intr-regs=\?. To name registers, pass a comma separated list such as
--intr-regs=ax,bx. The list of register is architecture dependent.

--user-regs::
Similar to -I, but capture user registers at sample time. To list the available
user registers use --user-regs=\?.

--running-time::
Record running and enabled time for read events (:S)

-k::
--clockid::
Sets the clock id to use for the various time fields in the perf_event_type
records. See clock_gettime(). In particular CLOCK_MONOTONIC and
CLOCK_MONOTONIC_RAW are supported, some events might also allow
CLOCK_BOOTTIME, CLOCK_REALTIME and CLOCK_TAI.

-S::
--snapshot::
Select AUX area tracing Snapshot Mode. This option is valid only with an
AUX area tracing event. Optionally, certain snapshot capturing parameters
can be specified in a string that follows this option:
  'e': take one last snapshot on exit; guarantees that there is at least one
       snapshot in the output file;
  <size>: if the PMU supports this, specify the desired snapshot size.

In Snapshot Mode trace data is captured only when signal SIGUSR2 is received
and on exit if the above 'e' option is given.

--aux-sample[=OPTIONS]::
Select AUX area sampling. At least one of the events selected by the -e option
must be an AUX area event. Samples on other events will be created containing
data from the AUX area. Optionally sample size may be specified, otherwise it
defaults to 4KiB.

--proc-map-timeout::
When processing pre-existing threads /proc/XXX/mmap, it may take a long time,
because the file may be huge. A time out is needed in such cases.
This option sets the time out limit. The default value is 500 ms.

--switch-events::
Record context switch events i.e. events of type PERF_RECORD_SWITCH or
PERF_RECORD_SWITCH_CPU_WIDE. In some cases (e.g. Intel PT, CoreSight or Arm SPE)
switch events will be enabled automatically, which can be suppressed by
by the option --no-switch-events.

--clang-path=PATH::
Path to clang binary to use for compiling BPF scriptlets.
(enabled when BPF support is on)

--clang-opt=OPTIONS::
Options passed to clang when compiling BPF scriptlets.
(enabled when BPF support is on)

--vmlinux=PATH::
Specify vmlinux path which has debuginfo.
(enabled when BPF prologue is on)

--buildid-all::
Record build-id of all DSOs regardless whether it's actually hit or not.

--buildid-mmap::
Record build ids in mmap2 events, disables build id cache (implies --no-buildid).

--aio[=n]::
Use <n> control blocks in asynchronous (Posix AIO) trace writing mode (default: 1, max: 4).
Asynchronous mode is supported only when linking Perf tool with libc library
providing implementation for Posix AIO API.

--affinity=mode::
Set affinity mask of trace reading thread according to the policy defined by 'mode' value:
  node - thread affinity mask is set to NUMA node cpu mask of the processed mmap buffer
  cpu  - thread affinity mask is set to cpu of the processed mmap buffer

--mmap-flush=number::

Specify minimal number of bytes that is extracted from mmap data pages and
processed for output. One can specify the number using B/K/M/G suffixes.

The maximal allowed value is a quarter of the size of mmaped data pages.

The default option value is 1 byte which means that every time that the output
writing thread finds some new data in the mmaped buffer the data is extracted,
possibly compressed (-z) and written to the output, perf.data or pipe.

Larger data chunks are compressed more effectively in comparison to smaller
chunks so extraction of larger chunks from the mmap data pages is preferable
from the perspective of output size reduction.

Also at some cases executing less output write syscalls with bigger data size
can take less time than executing more output write syscalls with smaller data
size thus lowering runtime profiling overhead.

-z::
--compression-level[=n]::
Produce compressed trace using specified level n (default: 1 - fastest compression,
22 - smallest trace)

--all-kernel::
Configure all used events to run in kernel space.

--all-user::
Configure all used events to run in user space.

--kernel-callchains::
Collect callchains only from kernel space. I.e. this option sets
perf_event_attr.exclude_callchain_user to 1.

--user-callchains::
Collect callchains only from user space. I.e. this option sets
perf_event_attr.exclude_callchain_kernel to 1.

Don't use both --kernel-callchains and --user-callchains at the same time or no
callchains will be collected.

--timestamp-filename
Append timestamp to output file name.

--timestamp-boundary::
Record timestamp boundary (time of first/last samples).

--switch-output[=mode]::
Generate multiple perf.data files, timestamp prefixed, switching to a new one
based on 'mode' value:
  "signal" - when receiving a SIGUSR2 (default value) or
  <size>   - when reaching the size threshold, size is expected to
             be a number with appended unit character - B/K/M/G
  <time>   - when reaching the time threshold, size is expected to
             be a number with appended unit character - s/m/h/d

             Note: the precision of  the size  threshold  hugely depends
             on your configuration  - the number and size of  your  ring
             buffers (-m). It is generally more precise for higher sizes
             (like >5M), for lower values expect different sizes.

A possible use case is to, given an external event, slice the perf.data file
that gets then processed, possibly via a perf script, to decide if that
particular perf.data snapshot should be kept or not.

Implies --timestamp-filename, --no-buildid and --no-buildid-cache.
The reason for the latter two is to reduce the data file switching
overhead. You can still switch them on with:

  --switch-output --no-no-buildid  --no-no-buildid-cache

--switch-output-event::
Events that will cause the switch of the perf.data file, auto-selecting
--switch-output=signal, the results are similar as internally the side band
thread will also send a SIGUSR2 to the main one.

Uses the same syntax as --event, it will just not be recorded, serving only to
switch the perf.data file as soon as the --switch-output event is processed by
a separate sideband thread.

This sideband thread is also used to other purposes, like processing the
PERF_RECORD_BPF_EVENT records as they happen, asking the kernel for extra BPF
information, etc.

--switch-max-files=N::

When rotating perf.data with --switch-output, only keep N files.

--dry-run::
Parse options then exit. --dry-run can be used to detect errors in cmdline
options.

'perf record --dry-run -e' can act as a BPF script compiler if llvm.dump-obj
in config file is set to true.

--synth=TYPE::
Collect and synthesize given type of events (comma separated).  Note that
this option controls the synthesis from the /proc filesystem which represent
task status for pre-existing threads.

Kernel (and some other) events are recorded regardless of the
choice in this option.  For example, --synth=no would have MMAP events for
kernel and modules.

Available types are:
  'task'    - synthesize FORK and COMM events for each task
  'mmap'    - synthesize MMAP events for each process (implies 'task')
  'cgroup'  - synthesize CGROUP events for each cgroup
  'all'     - synthesize all events (default)
  'no'      - do not synthesize any of the above events

--tail-synthesize::
Instead of collecting non-sample events (for example, fork, comm, mmap) at
the beginning of record, collect them during finalizing an output file.
The collected non-sample events reflects the status of the system when
record is finished.

--overwrite::
Makes all events use an overwritable ring buffer. An overwritable ring
buffer works like a flight recorder: when it gets full, the kernel will
overwrite the oldest records, that thus will never make it to the
perf.data file.

When '--overwrite' and '--switch-output' are used perf records and drops
events until it receives a signal, meaning that something unusual was
detected that warrants taking a snapshot of the most current events,
those fitting in the ring buffer at that moment.

'overwrite' attribute can also be set or canceled for an event using
config terms. For example: 'cycles/overwrite/' and 'instructions/no-overwrite/'.

Implies --tail-synthesize.

--kcore::
Make a copy of /proc/kcore and place it into a directory with the perf data file.

--max-size=<size>::
Limit the sample data max size, <size> is expected to be a number with
appended unit character - B/K/M/G

--num-thread-synthesize::
	The number of threads to run when synthesizing events for existing processes.
	By default, the number of threads equals 1.

ifdef::HAVE_LIBPFM[]
--pfm-events events::
Select a PMU event using libpfm4 syntax (see http://perfmon2.sf.net)
including support for event filters. For example '--pfm-events
inst_retired:any_p:u:c=1:i'. More than one event can be passed to the
option using the comma separator. Hardware events and generic hardware
events cannot be mixed together. The latter must be used with the -e
option. The -e option and this one can be mixed and matched.  Events
can be grouped using the {} notation.
endif::HAVE_LIBPFM[]

--control=fifo:ctl-fifo[,ack-fifo]::
--control=fd:ctl-fd[,ack-fd]::
ctl-fifo / ack-fifo are opened and used as ctl-fd / ack-fd as follows.
Listen on ctl-fd descriptor for command to control measurement.

Available commands:
  'enable'           : enable events
  'disable'          : disable events
  'enable name'      : enable event 'name'
  'disable name'     : disable event 'name'
  'snapshot'         : AUX area tracing snapshot).
  'stop'             : stop perf record
  'ping'             : ping

  'evlist [-v|-g|-F] : display all events
                       -F  Show just the sample frequency used for each event.
                       -v  Show all fields.
                       -g  Show event group information.

Measurements can be started with events disabled using --delay=-1 option. Optionally
send control command completion ('ack\n') to ack-fd descriptor to synchronize with the
controlling process.  Example of bash shell script to enable and disable events during
measurements:

 #!/bin/bash

 ctl_dir=/tmp/

 ctl_fifo=${ctl_dir}perf_ctl.fifo
 test -p ${ctl_fifo} && unlink ${ctl_fifo}
 mkfifo ${ctl_fifo}
 exec {ctl_fd}<>${ctl_fifo}

 ctl_ack_fifo=${ctl_dir}perf_ctl_ack.fifo
 test -p ${ctl_ack_fifo} && unlink ${ctl_ack_fifo}
 mkfifo ${ctl_ack_fifo}
 exec {ctl_fd_ack}<>${ctl_ack_fifo}

 perf record -D -1 -e cpu-cycles -a               \
             --control fd:${ctl_fd},${ctl_fd_ack} \
             -- sleep 30 &
 perf_pid=$!

 sleep 5  && echo 'enable' >&${ctl_fd} && read -u ${ctl_fd_ack} e1 && echo "enabled(${e1})"
 sleep 10 && echo 'disable' >&${ctl_fd} && read -u ${ctl_fd_ack} d1 && echo "disabled(${d1})"

 exec {ctl_fd_ack}>&-
 unlink ${ctl_ack_fifo}

 exec {ctl_fd}>&-
 unlink ${ctl_fifo}

 wait -n ${perf_pid}
 exit $?

--threads=<spec>::
Write collected trace data into several data files using parallel threads.
<spec> value can be user defined list of masks. Masks separated by colon
define CPUs to be monitored by a thread and affinity mask of that thread
is separated by slash:

    <cpus mask 1>/<affinity mask 1>:<cpus mask 2>/<affinity mask 2>:...

CPUs or affinity masks must not overlap with other corresponding masks.
Invalid CPUs are ignored, but masks containing only invalid CPUs are not
allowed.

For example user specification like the following:

    0,2-4/2-4:1,5-7/5-7

specifies parallel threads layout that consists of two threads,
the first thread monitors CPUs 0 and 2-4 with the affinity mask 2-4,
the second monitors CPUs 1 and 5-7 with the affinity mask 5-7.

<spec> value can also be a string meaning predefined parallel threads
layout:

    cpu    - create new data streaming thread for every monitored cpu
    core   - create new thread to monitor CPUs grouped by a core
    package - create new thread to monitor CPUs grouped by a package
    numa   - create new threed to monitor CPUs grouped by a NUMA domain

Predefined layouts can be used on systems with large number of CPUs in
order not to spawn multiple per-cpu streaming threads but still avoid LOST
events in data directory files. Option specified with no or empty value
defaults to CPU layout. Masks defined or provided by the option value are
filtered through the mask provided by -C option.

--debuginfod[=URLs]::
	Specify debuginfod URL to be used when cacheing perf.data binaries,
	it follows the same syntax as the DEBUGINFOD_URLS variable, like:

	  http://192.168.122.174:8002

	If the URLs is not specified, the value of DEBUGINFOD_URLS
	system environment variable is used.

--off-cpu::
	Enable off-cpu profiling with BPF.  The BPF program will collect
	task scheduling information with (user) stacktrace and save them
	as sample data of a software event named "offcpu-time".  The
	sample period will have the time the task slept in nanoseconds.

	Note that BPF can collect stack traces using frame pointer ("fp")
	only, as of now.  So the applications built without the frame
	pointer might see bogus addresses.

include::intel-hybrid.txt[]

SEE ALSO
--------
linkperf:perf-stat[1], linkperf:perf-list[1], linkperf:perf-intel-pt[1]