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+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]