# perf-diff

## 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 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.
    


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