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HTML rendering created 2023-12-22 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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NAME | SYNOPSIS | DESCRIPTION | OPTIONS | INTERACTIVE PROMPTING KEYS | OVERHEAD CALCULATION | SEE ALSO | COLOPHON |
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PERF-TOP(1) perf Manual PERF-TOP(1)
perf-top - System profiling tool.
perf top [-e <EVENT> | --event=EVENT] [<options>]
This command generates and displays a performance counter profile
in real time.
-a, --all-cpus
System-wide collection. (default)
-c <count>, --count=<count>
Event period to sample.
-C <cpu-list>, --cpu=<cpu>
Monitor 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. Default is to
monitor all CPUS.
-d <seconds>, --delay=<seconds>
Number of seconds to delay between refreshes.
-e <event>, --event=<event>
Select the PMU event. Selection can be a symbolic event name
(use perf list to list all events) or 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/*.
-E <entries>, --entries=<entries>
Display this many functions.
-f <count>, --count-filter=<count>
Only display functions with more events than this.
--group-sort-idx
Sort the output by the event at the index n in group. If n is
invalid, sort by the first event. It can support multiple
groups with different amount of events. WARNING: This should
be used on grouped events.
-F <freq>, --freq=<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.
-i, --inherit
Child tasks do not inherit counters.
-k <path>, --vmlinux=<path>
Path to vmlinux. Required for annotation functionality.
--ignore-vmlinux
Ignore vmlinux files.
--kallsyms=<file>
kallsyms pathname
-m <pages>, --mmap-pages=<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.
-p <pid>, --pid=<pid>
Profile events on existing Process ID (comma separated list).
-t <tid>, --tid=<tid>
Profile events on existing thread ID (comma separated list).
-u, --uid=
Record events in threads owned by uid. Name or number.
-r <priority>, --realtime=<priority>
Collect data with this RT SCHED_FIFO priority.
--sym-annotate=<symbol>
Annotate this symbol.
-K, --hide_kernel_symbols
Hide kernel symbols.
-U, --hide_user_symbols
Hide user symbols.
--demangle-kernel
Demangle kernel symbols.
-D, --dump-symtab
Dump the symbol table used for profiling.
-v, --verbose
Be more verbose (show counter open errors, etc).
-z, --zero
Zero history across display updates.
-s, --sort
Sort by key(s): pid, comm, dso, symbol, parent, srcline,
weight, local_weight, abort, in_tx, transaction, overhead,
sample, period. Please see description of --sort in the
perf-report man page.
--fields=
Specify output field - multiple keys can be specified in CSV
format. Following fields are available: overhead,
overhead_sys, overhead_us, overhead_children, sample and
period. Also it can contain any sort key(s).
By default, every sort keys not specified in --field will be appended
automatically.
-n, --show-nr-samples
Show a column with the number of samples.
--show-total-period
Show a column with the sum of periods.
--dsos
Only consider symbols in these dsos. This option will affect
the percentage of the overhead column. See --percentage for
more info.
--comms
Only consider symbols in these comms. This option will affect
the percentage of the overhead column. See --percentage for
more info.
--symbols
Only consider these symbols. This option will affect the
percentage of the overhead column. See --percentage for more
info.
-M, --disassembler-style=
Set disassembler style for objdump.
--addr2line=<path>
Path to addr2line binary.
--objdump=<path>
Path to objdump binary.
--prefix=PREFIX, --prefix-strip=N
Remove first N entries from source file path names in
executables and add PREFIX. This allows to display source
code compiled on systems with different file system layout.
--source
Interleave source code with assembly code. Enabled by
default, disable with --no-source.
--asm-raw
Show raw instruction encoding of assembly instructions.
-g
Enables call-graph (stack chain/backtrace) recording.
--call-graph [mode,type,min[,limit],order[,key][,branch]]
Setup and enable call-graph (stack chain/backtrace)
recording, implies -g. See --call-graph section in
perf-record and perf-report man pages for details.
--children
Accumulate callchain of children to parent entry so that then
can show up in the output. The output will have a new
"Children" column and will be sorted on the data. It requires
-g/--call-graph option enabled. See the ‘overhead
calculation’ section for more details. Enabled by default,
disable with --no-children.
--max-stack
Set the stack depth limit when parsing the callchain,
anything beyond the specified depth will be ignored. This is
a trade-off between information loss and faster processing
especially for workloads that can have a very long callchain
stack.
Default: /proc/sys/kernel/perf_event_max_stack when present, 127 otherwise.
--ignore-callees=<regex>
Ignore callees of the function(s) matching the given regex.
This has the effect of collecting the callers of each such
function into one place in the call-graph tree.
--percent-limit
Do not show entries which have an overhead under that
percent. (Default: 0).
--percentage
Determine how to display the overhead percentage of filtered
entries. Filters can be applied by --comms, --dsos and/or
--symbols options and Zoom operations on the TUI (thread,
dso, etc).
"relative" means it's relative to filtered entries only so that the
sum of shown entries will be always 100%. "absolute" means it retains
the original value before and after the filter is applied.
-w, --column-widths=<width[,width...]>
Force each column width to the provided list, for large
terminal readability. 0 means no limit (default behavior).
--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.
-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. For a full list of modifiers please see the
perf record manpage.
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.
--branch-history
Add the addresses of sampled taken branches to the callstack.
This allows to examine the path the program took to each
sample.
--raw-trace
When displaying traceevent output, do not use print fmt or
plugins.
--hierarchy
Enable hierarchy output.
--overwrite
Enable this to use just the most recent records, which helps
in high core count machines such as Knights Landing/Mill, but
right now is disabled by default as the pausing used in this
technique is leading to loss of metadata events such as
PERF_RECORD_MMAP which makes perf top unable to resolve
samples, leading to lots of unknown samples appearing on the
UI. Enable this if you are in such machines and profiling a
workload that doesn’t creates short lived threads and/or
doesn’t uses many executable mmap operations. Work is being
planed to solve this situation, till then, this will remain
disabled by default.
--force
Don’t do ownership validation.
--num-thread-synthesize
The number of threads to run when synthesizing events for
existing processes. By default, the number of threads equals
to the number of online CPUs.
--namespaces
Record events of type PERF_RECORD_NAMESPACES and display it
with the cgroup_id sort key.
-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.
--all-cgroups
Record events of type PERF_RECORD_CGROUP and display it with
the cgroup sort key.
--switch-on EVENT_NAME
Only consider events after this event is found.
E.g.:
Find out where broadcast packets are handled
perf probe -L icmp_rcv
Insert a probe there:
perf probe icmp_rcv:59
Start perf top and ask it to only consider the cycles events when a
broadcast packet arrives This will show a menu with two entries and
will start counting when a broadcast packet arrives:
perf top -e cycles,probe:icmp_rcv --switch-on=probe:icmp_rcv
Alternatively one can ask for a group and then two overhead columns
will appear, the first for cycles and the second for the switch-on event.
perf top -e '{cycles,probe:icmp_rcv}' --switch-on=probe:icmp_rcv
This may be interesting to measure a workload only after some initialization
phase is over, i.e. insert a perf probe at that point and use the above
examples replacing probe:icmp_rcv with the just-after-init probe.
--switch-off EVENT_NAME
Stop considering events after this event is found.
--show-on-off-events
Show the --switch-on/off events too. This has no effect in
perf top now but probably we’ll make the default not to show
the switch-on/off events on the --group mode and if there is
only one event besides the off/on ones, go straight to the
histogram browser, just like perf top with no events
explicitly specified does.
--stitch-lbr
Show callgraph with stitched LBRs, which may have more
complete callgraph. The option must be used with --call-graph
lbr recording. Disabled by default. In common cases with call
stack overflows, it can recreate better call stacks than the
default lbr call stack output. But this approach is not
foolproof. There can be cases where it creates incorrect call
stacks from incorrect matches. The known limitations include
exception handing such as setjmp/longjmp will have
calls/returns not match.
[d]
Display refresh delay.
[e]
Number of entries to display.
[E]
Event to display when multiple counters are active.
[f]
Profile display filter (>= hit count).
[F]
Annotation display filter (>= % of total).
[s]
Annotate symbol.
[S]
Stop annotation, return to full profile display.
[K]
Hide kernel symbols.
[U]
Hide user symbols.
[z]
Toggle event count zeroing across display updates.
[qQ]
Quit.
Pressing any unmapped key displays a menu, and prompts for input.
The overhead can be shown in two columns as Children and Self
when perf collects callchains. The self overhead is simply
calculated by adding all period values of the entry - usually a
function (symbol). This is the value that perf shows
traditionally and sum of all the self overhead values should be
100%.
The children overhead is calculated by adding all period values
of the child functions so that it can show the total overhead of
the higher level functions even if they don’t directly execute
much. Children here means functions that are called from another
(parent) function.
It might be confusing that the sum of all the children overhead
values exceeds 100% since each of them is already an accumulation
of self overhead of its child functions. But with this enabled,
users can find which function has the most overhead even if
samples are spread over the children.
Consider the following example; there are three functions like
below.
.ft C
void foo(void) {
/* do something */
}
void bar(void) {
/* do something */
foo();
}
int main(void) {
bar()
return 0;
}
.ft
In this case foo is a child of bar, and bar is an immediate child
of main so foo also is a child of main. In other words, main is a
parent of foo and bar, and bar is a parent of foo.
Suppose all samples are recorded in foo and bar only. When it’s
recorded with callchains the output will show something like
below in the usual (self-overhead-only) output of perf report:
.ft C
Overhead Symbol
........ .....................
60.00% foo
|
--- foo
bar
main
__libc_start_main
40.00% bar
|
--- bar
main
__libc_start_main
.ft
When the --children option is enabled, the self overhead values
of child functions (i.e. foo and bar) are added to the parents to
calculate the children overhead. In this case the report could be
displayed as:
.ft C
Children Self Symbol
........ ........ ....................
100.00% 0.00% __libc_start_main
|
--- __libc_start_main
100.00% 0.00% main
|
--- main
__libc_start_main
100.00% 40.00% bar
|
--- bar
main
__libc_start_main
60.00% 60.00% foo
|
--- foo
bar
main
__libc_start_main
.ft
In the above output, the self overhead of foo (60%) was add to
the children overhead of bar, main and __libc_start_main.
Likewise, the self overhead of bar (40%) was added to the
children overhead of main and \_\_libc_start_main.
So \_\_libc_start_main and main are shown first since they have
same (100%) children overhead (even though they have zero self
overhead) and they are the parents of foo and bar.
Since v3.16 the children overhead is shown by default and the
output is sorted by its values. The children overhead is disabled
by specifying --no-children option on the command line or by
adding report.children = false or top.children = false in the
perf config file.
perf-stat(1), perf-list(1), perf-report(1)
This page is part of the perf (Performance analysis tools for
Linux (in Linux source tree)) project. Information about the
project can be found at
⟨https://perf.wiki.kernel.org/index.php/Main_Page⟩. If you have a
bug report for this manual page, send it to
linux-kernel@vger.kernel.org. This page was obtained from the
project's upstream Git repository
⟨http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git⟩
on 2023-12-22. (At that time, the date of the most recent commit
that was found in the repository was 2023-12-21.) If you
discover any rendering problems in this HTML version of the page,
or you believe there is a better or more up-to-date source for
the page, or you have corrections or improvements to the
information in this COLOPHON (which is not part of the original
manual page), send a mail to man-pages@man7.org
perf 2023-04-04 PERF-TOP(1)
Pages that refer to this page: perf(1), perf-buildid-list(1), perf-kvm(1), perf-list(1), perf-stat(1)
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HTML rendering created 2023-12-22 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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