NAME
perf-diff - Read perf.data files and display the differential profileSYNOPSIS
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.OPTIONS
-D, --dump-raw-traceDump raw trace in ASCII.
kallsyms pathname
Load module symbols. WARNING: use only with -k
and LIVE kernel
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.
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.
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.
Sort by key(s): pid, comm, dso, symbol, cpu,
parent, srcline. Please see description of --sort in the perf-report man
page.
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.
Be verbose, for instance, show the raw counts
in addition to the diff.
Do not show any warnings or messages.
(Suppress -v)
Don’t do ownership validation.
Look for files with symbols relative to this
directory.
Show only items with match in baseline.
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.
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.
Show period values for both compared hist
entries.
Show formula for given computation.
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.
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.
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.
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.
Only diff samples for given process ID (comma
separated list).
Only diff samples for given thread ID (comma
separated list).
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.•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
•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
•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.SEE ALSO
perf-record(1), perf-report(1)2024-06-21 | perf |