OPTIONS¶
-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
(eventsel+umask) in the form of rNNN where NNN is a hexadecimal event
descriptor.
-E <entries>, --entries=<entries>
Display this many functions.
-f <count>, --count-filter=<count>
Only display functions with more events than this.
--group
Put the counters into a counter group.
--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.
--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.
--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.
Find out where broadcast packets are handled
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 --group and then two overhead columns
will appear, the first for cycles and the second for the switch-on event.
perf top --group -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 full proof. 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.
OVERHEAD CALCULATION¶
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.