perf-top - Online in the Cloud

PROGRAM:

NAME

perf-top - System profiling tool.

SYNOPSIS

perf top [-e <EVENT> | --event=EVENT] [<options>]

DESCRIPTION

This command generates and displays a performance counter profile in real time.

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.

-F <freq>, --freq=<freq>
Profile at this frequency.

-i, --inherit
Child tasks do not inherit counters.

-k <path>, --vmlinux=<path>
Path to vmlinux. Required for annotation functionality.

-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.

--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.

--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: 127

--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.

INTERACTIVE PROMPTING KEYS

[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.

[z]
Toggle event count zeroing across display updates.

[qQ]
Quit.

Pressing any unmapped key displays a menu, and prompts for input.

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.

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