perf-report - Online in the Cloud

PROGRAM:

NAME

perf-report - Read perf.data (created by perf record) and display the profile

SYNOPSIS

perf report [-i <file> | --input=file]

DESCRIPTION

This command displays the performance counter profile information recorded via perf
record.

OPTIONS

-i, --input=
Input file name. (default: perf.data unless stdin is a fifo)

-v, --verbose
Be more verbose. (show symbol address, etc)

-n, --show-nr-samples
Show the number of samples for each symbol

--show-cpu-utilization
Show sample percentage for different cpu modes.

-T, --threads
Show per-thread event counters. The input data file should be recorded with -s option.

-c, --comms=
Only consider symbols in these comms. CSV that understands file://filename entries.
This option will affect the percentage of the overhead column. See --percentage for
more info.

--pid=
Only show events for given process ID (comma separated list).

--tid=
Only show events for given thread ID (comma separated list).

-d, --dsos=
Only consider symbols in these dsos. CSV that understands file://filename entries.
This option will affect the percentage of the overhead column. See --percentage for
more info.

-S, --symbols=
Only consider these symbols. CSV that understands file://filename entries. This option
will affect the percentage of the overhead column. See --percentage for more info.

--symbol-filter=
Only show symbols that match (partially) with this filter.

-U, --hide-unresolved
Only display entries resolved to a symbol.

-s, --sort=
Sort histogram entries by given key(s) - multiple keys can be specified in CSV format.
Following sort keys are available: pid, comm, dso, symbol, parent, cpu, socket,
srcline, weight, local_weight.

Each key has following meaning:

· comm: command (name) of the task which can be read via /proc/<pid>/comm

· pid: command and tid of the task

· dso: name of library or module executed at the time of sample

· symbol: name of function executed at the time of sample

· parent: name of function matched to the parent regex filter. Unmatched entries are
displayed as "[other]".

· cpu: cpu number the task ran at the time of sample

· socket: processor socket number the task ran at the time of sample

· srcline: filename and line number executed at the time of sample. The DWARF
debugging info must be provided.

· srcfile: file name of the source file of the same. Requires dwarf information.

· weight: Event specific weight, e.g. memory latency or transaction abort cost. This
is the global weight.

· local_weight: Local weight version of the weight above.

· transaction: Transaction abort flags.

· overhead: Overhead percentage of sample

· overhead_sys: Overhead percentage of sample running in system mode

· overhead_us: Overhead percentage of sample running in user mode

· overhead_guest_sys: Overhead percentage of sample running in system mode on guest
machine

· overhead_guest_us: Overhead percentage of sample running in user mode on guest
machine

· sample: Number of sample

· period: Raw number of event count of sample

By default, comm, dso and symbol keys are used.
(i.e. --sort comm,dso,symbol)

If --branch-stack option is used, following sort keys are also
available:
dso_from, dso_to, symbol_from, symbol_to, mispredict.

· dso_from: name of library or module branched from

· dso_to: name of library or module branched to

· symbol_from: name of function branched from

· symbol_to: name of function branched to

· mispredict: "N" for predicted branch, "Y" for mispredicted branch

· in_tx: branch in TSX transaction

· abort: TSX transaction abort.

· cycles: Cycles in basic block

And default sort keys are changed to comm, dso_from, symbol_from, dso_to
and symbol_to, see '--branch-stack'.

-F, --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 -F will be appended
automatically.

If --mem-mode option is used, following sort keys are also available
(incompatible with --branch-stack):
symbol_daddr, dso_daddr, locked, tlb, mem, snoop, dcacheline.

· symbol_daddr: name of data symbol being executed on at the time of sample

· dso_daddr: name of library or module containing the data being executed on at the
time of sample

· locked: whether the bus was locked at the time of sample

· tlb: type of tlb access for the data at the time of sample

· mem: type of memory access for the data at the time of sample

· snoop: type of snoop (if any) for the data at the time of sample

· dcacheline: the cacheline the data address is on at the time of sample

And default sort keys are changed to local_weight, mem, sym, dso,
symbol_daddr, dso_daddr, snoop, tlb, locked, see '--mem-mode'.

-p, --parent=<regex>
A regex filter to identify parent. The parent is a caller of this function and
searched through the callchain, thus it requires callchain information recorded. The
pattern is in the exteneded regex format and defaults to "^sys_|^do_page_fault", see
--sort parent.

-x, --exclude-other
Only display entries with parent-match.

-w, --column-widths=<width[,width...]>
Force each column width to the provided list, for large terminal readability. 0 means
no limit (default behavior).

-t, --field-separator=
Use a special separator character and don’t pad with spaces, replacing all occurrences
of this separator in symbol names (and other output) with a . character, that thus
it’s the only non valid separator.

-D, --dump-raw-trace
Dump raw trace in ASCII.

-g, --call-graph=<print_type,threshold[,print_limit],order,sort_key,branch>
Display call chains using type, min percent threshold, print limit, call order, sort
key and branch. Note that ordering of parameters is not fixed so any parement can be
given in an arbitraty order. One exception is the print_limit which should be preceded
by threshold.

print_type can be either:
- flat: single column, linear exposure of call chains.
- graph: use a graph tree, displaying absolute overhead rates. (default)
- fractal: like graph, but displays relative rates. Each branch of
the tree is considered as a new profiled object.
- none: disable call chain display.

threshold is a percentage value which specifies a minimum percent to be
included in the output call graph. Default is 0.5 (%).

print_limit is only applied when stdio interface is used. It's to limit
number of call graph entries in a single hist entry. Note that it needs
to be given after threshold (but not necessarily consecutive).
Default is 0 (unlimited).

order can be either:
- callee: callee based call graph.
- caller: inverted caller based call graph.
Default is 'caller' when --children is used, otherwise 'callee'.

sort_key can be:
- function: compare on functions (default)
- address: compare on individual code addresses

branch can be:
- branch: include last branch information in callgraph when available.
Usually more convenient to use --branch-history for this.

--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 callchains are recorded. 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. Note
that when using the --itrace option the synthesized callchain size will override this
value if the synthesized callchain size is bigger.

Default: 127

-G, --inverted
alias for inverted caller based call graph.

--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.

--pretty=<key>
Pretty printing style. key: normal, raw

--stdio
Use the stdio interface.

--tui
Use the TUI interface, that is integrated with annotate and allows zooming into DSOs
or threads, among other features. Use of --tui requires a tty, if one is not present,
as when piping to other commands, the stdio interface is used.

--gtk
Use the GTK2 interface.

-k, --vmlinux=<file>
vmlinux pathname

--kallsyms=<file>
kallsyms pathname

-m, --modules
Load module symbols. WARNING: This should only be used with -k and a LIVE kernel.

-f, --force
Don’t complain, do it.

--symfs=<directory>
Look for files with symbols relative to this directory.

-C, --cpu
Only report samples for 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 report samples on all CPUs.

-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.

--show-total-period
Show a column with the sum of periods.

-I, --show-info
Display extended information about the perf.data file. This adds information which may
be very large and thus may clutter the display. It currently includes: cpu and numa
topology of the host system.

-b, --branch-stack
Use the addresses of sampled taken branches instead of the instruction address to
build the histograms. To generate meaningful output, the perf.data file must have been
obtained using perf record -b or perf record --branch-filter xxx where xxx is a branch
filter option. perf report is able to auto-detect whether a perf.data file contains
branch stacks and it will automatically switch to the branch view mode, unless
--no-branch-stack is used.

--branch-history
Add the addresses of sampled taken branches to the callstack. This allows to examine
the path the program took to each sample. The data collection must have used -b (or
-j) and -g.

--objdump=<path>
Path to objdump binary.

--group
Show event group information together.

--demangle
Demangle symbol names to human readable form. It’s enabled by default, disable with
--no-demangle.

--demangle-kernel
Demangle kernel symbol names to human readable form (for C++ kernels).

--mem-mode
Use the data addresses of samples in addition to instruction addresses to build the
histograms. To generate meaningful output, the perf.data file must have been obtained
using perf record -d -W and using a special event -e cpu/mem-loads/ or -e
cpu/mem-stores/. See perf mem for simpler access.

--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.

--header
Show header information in the perf.data file. This includes various information like
hostname, OS and perf version, cpu/mem info, perf command line, event list and so on.
Currently only --stdio output supports this feature.

--header-only
Show only perf.data header (forces --stdio).

--itrace
Options for decoding instruction tracing data. The options are:

i synthesize instructions events
b synthesize branches events
c synthesize branches events (calls only)
r synthesize branches events (returns only)
x synthesize transactions events
e synthesize error events
d create a debug log
g synthesize a call chain (use with i or x)
l synthesize last branch entries (use with i or x)

The default is all events i.e. the same as --itrace=ibxe

In addition, the period (default 100000) for instructions events
can be specified in units of:

i instructions
t ticks
ms milliseconds
us microseconds
ns nanoseconds (default)

Also the call chain size (default 16, max. 1024) for instructions or
transactions events can be specified.

Also the number of last branch entries (default 64, max. 1024) for
instructions or transactions events can be specified.

To disable decoding entirely, use --no-itrace.

--full-source-path
Show the full path for source files for srcline output.

--show-ref-call-graph
When multiple events are sampled, it may not be needed to collect callgraphs for all
of them. The sample sites are usually nearby, and it’s enough to collect the
callgraphs on a reference event. So user can use "call-graph=no" event modifier to
disable callgraph for other events to reduce the overhead. However, perf report cannot
show callgraphs for the event which disable the callgraph. This option extends the
perf report to show reference callgraphs, which collected by reference event, in no
callgraph event.

--socket-filter
Only report the samples on the processor socket that match with this filter

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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