perf-diff.txt

perf-diff(1)
============

NAME
----
perf-diff - Read perf.data files and display the differential profile

SYNOPSIS
--------
[verse]
'perf diff' [baseline file] [data file1] [[data file2] ... ]

DESCRIPTION
-----------
This command displays the performance difference amongst two or more perf.data
files captured via perf record.

If no parameters are passed it will assume perf.data.old and perf.data.

The differential profile is displayed only for events matching both
specified perf.data files.

If no parameters are passed the samples will be sorted by dso and symbol.
As the perf.data files could come from different binaries, the symbols addresses
could vary. So perf diff is based on the comparison of the files and
symbols name.

OPTIONS
-------
-D::
--dump-raw-trace::
        Dump raw trace in ASCII.

--kallsyms=<file>::
        kallsyms pathname

-m::
--modules::
        Load module symbols. WARNING: use only with -k and LIVE kernel

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

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

-s::
--sort=::
	Sort by key(s): pid, comm, dso, symbol, cpu, parent, srcline.
	Please see description of --sort in the perf-report man page.

-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.

-v::
--verbose::
	Be verbose, for instance, show the raw counts in addition to the
	diff.

-q::
--quiet::
	Do not show any warnings or messages.  (Suppress -v)

-f::
--force::
        Don't do ownership validation.

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

-b::
--baseline-only::
        Show only items with match in baseline.

-c::
--compute::
        Differential computation selection - delta, ratio, wdiff, cycles,
        delta-abs (default is delta-abs).  Default can be changed using
        diff.compute config option.  See COMPARISON METHODS section for
        more info.

--cycles-hist::
	Report a histogram and the standard deviation for cycles data.
	It can help us to judge if the reported cycles data is noisy or
	not. This option should be used with '-c cycles'.

-p::
--period::
        Show period values for both compared hist entries.

-F::
--formula::
        Show formula for given computation.

-o::
--order::
       Specify compute sorting column number.  0 means sorting by baseline
       overhead and 1 (default) means sorting by computed value of column 1
       (data from the first file other base baseline).  Values more than 1
       can be used only if enough data files are provided.
       The default value can be set using the diff.order config option.

--percentage::
	Determine how to display the overhead percentage of filtered entries.
	Filters can be applied by --comms, --dsos and/or --symbols options.

	"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.

--time::
	Analyze samples within given time window. It supports time
	percent with multiple time ranges. Time string is 'a%/n,b%/m,...'
	or 'a%-b%,c%-%d,...'.

	For example:

	Select the second 10% time slice to diff:

	  perf diff --time 10%/2

	Select from 0% to 10% time slice to diff:

	  perf diff --time 0%-10%

	Select the first and the second 10% time slices to diff:

	  perf diff --time 10%/1,10%/2

	Select from 0% to 10% and 30% to 40% slices to diff:

	  perf diff --time 0%-10%,30%-40%

	It also supports analyzing samples within a given time window
	<start>,<stop>. Times have the format seconds.nanoseconds. If 'start'
	is not given (i.e. time string is ',x.y') then analysis starts at
	the beginning of the file. If stop time is not given (i.e. time
	string is 'x.y,') then analysis goes to the end of the file.
	Multiple ranges can be separated by spaces, which requires the argument
	to be quoted e.g. --time "1234.567,1234.789 1235,"
	Time string is'a1.b1,c1.d1:a2.b2,c2.d2'. Use ':' to separate timestamps
	for different perf.data files.

	For example, we get the timestamp information from 'perf script'.

	  perf script -i perf.data.old
	    mgen 13940 [000]  3946.361400: ...

	  perf script -i perf.data
	    mgen 13940 [000]  3971.150589 ...

	  perf diff --time 3946.361400,:3971.150589,

	It analyzes the perf.data.old from the timestamp 3946.361400 to
	the end of perf.data.old and analyzes the perf.data from the
	timestamp 3971.150589 to the end of perf.data.

--cpu:: Only diff 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.

--pid=::
	Only diff samples for given process ID (comma separated list).

--tid=::
	Only diff samples for given thread ID (comma separated list).

--stream::
	Enable hot streams comparison. Stream can be a callchain which is
	aggregated by the branch records from samples.

COMPARISON
----------
The comparison is governed by the baseline file. The baseline perf.data
file is iterated for samples. All other perf.data files specified on
the command line are searched for the baseline sample pair. If the pair
is found, specified computation is made and result is displayed.

All samples from non-baseline perf.data files, that do not match any
baseline entry, are displayed with empty space within baseline column
and possible computation results (delta) in their related column.

Example files samples:
- file A with samples f1, f2, f3, f4,    f6
- file B with samples     f2,     f4, f5
- file C with samples f1, f2,         f5

Example output:
  x - computation takes place for pair
  b - baseline sample percentage

- perf diff A B C

  baseline/A compute/B compute/C  samples
  ---------------------------------------
  b                    x          f1
  b          x         x          f2
  b                               f3
  b          x                    f4
  b                               f6
             x         x          f5

- perf diff B A C

  baseline/B compute/A compute/C  samples
  ---------------------------------------
  b          x         x          f2
  b          x                    f4
  b                    x          f5
             x         x          f1
             x                    f3
             x                    f6

- perf diff C B A

  baseline/C compute/B compute/A  samples
  ---------------------------------------
  b                    x          f1
  b          x         x          f2
  b          x                    f5
                       x          f3
             x         x          f4
                       x          f6

COMPARISON METHODS
------------------
delta
~~~~~
If specified the 'Delta' column is displayed with value 'd' computed as:

  d = A->period_percent - B->period_percent

with:
  - A/B being matching hist entry from data/baseline file specified
    (or perf.data/perf.data.old) respectively.

  - period_percent being the % of the hist entry period value within
    single data file

  - with filtering by -C, -d and/or -S, period_percent might be changed
    relative to how entries are filtered.  Use --percentage=absolute to
    prevent such fluctuation.

delta-abs
~~~~~~~~~
Same as 'delta` method, but sort the result with the absolute values.

ratio
~~~~~
If specified the 'Ratio' column is displayed with value 'r' computed as:

  r = A->period / B->period

with:
  - A/B being matching hist entry from data/baseline file specified
    (or perf.data/perf.data.old) respectively.

  - period being the hist entry period value

wdiff:WEIGHT-B,WEIGHT-A
~~~~~~~~~~~~~~~~~~~~~~~
If specified the 'Weighted diff' column is displayed with value 'd' computed as:

   d = B->period * WEIGHT-A - A->period * WEIGHT-B

  - A/B being matching hist entry from data/baseline file specified
    (or perf.data/perf.data.old) respectively.

  - period being the hist entry period value

  - WEIGHT-A/WEIGHT-B being user supplied weights in the the '-c' option
    behind ':' separator like '-c wdiff:1,2'.
    - WEIGHT-A being the weight of the data file
    - WEIGHT-B being the weight of the baseline data file

cycles
~~~~~~
If specified the '[Program Block Range] Cycles Diff' column is displayed.
It displays the cycles difference of same program basic block amongst
two perf.data. The program basic block is the code between two branches.

'[Program Block Range]' indicates the range of a program basic block.
Source line is reported if it can be found otherwise uses symbol+offset
instead.

SEE ALSO
--------
linkperf:perf-record[1], linkperf:perf-report[1]