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NAME

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

SYNOPSIS

       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 message. (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, delta-abs (default is
           delta-abs). Default can be changed using diff.compute config option. See COMPARISON
           METHODS section for more info.

       -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.

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

SEE ALSO

       perf-record(1), perf-report(1)