306 lines
9.1 KiB
Plaintext
306 lines
9.1 KiB
Plaintext
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perf-diff(1)
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============
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NAME
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----
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perf-diff - Read perf.data files and display the differential profile
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SYNOPSIS
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--------
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[verse]
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'perf diff' [baseline file] [data file1] [[data file2] ... ]
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DESCRIPTION
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-----------
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This command displays the performance difference amongst two or more perf.data
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files captured via perf record.
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If no parameters are passed it will assume perf.data.old and perf.data.
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The differential profile is displayed only for events matching both
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specified perf.data files.
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If no parameters are passed the samples will be sorted by dso and symbol.
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As the perf.data files could come from different binaries, the symbols addresses
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could vary. So perf diff is based on the comparison of the files and
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symbols name.
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OPTIONS
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-------
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-D::
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--dump-raw-trace::
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Dump raw trace in ASCII.
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--kallsyms=<file>::
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kallsyms pathname
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-m::
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--modules::
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Load module symbols. WARNING: use only with -k and LIVE kernel
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-d::
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--dsos=::
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Only consider symbols in these dsos. CSV that understands
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file://filename entries. This option will affect the percentage
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of the Baseline/Delta column. See --percentage for more info.
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-C::
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--comms=::
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Only consider symbols in these comms. CSV that understands
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file://filename entries. This option will affect the percentage
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of the Baseline/Delta column. See --percentage for more info.
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-S::
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--symbols=::
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Only consider these symbols. CSV that understands
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file://filename entries. This option will affect the percentage
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of the Baseline/Delta column. See --percentage for more info.
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-s::
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--sort=::
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Sort by key(s): pid, comm, dso, symbol, cpu, parent, srcline.
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Please see description of --sort in the perf-report man page.
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-t::
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--field-separator=::
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Use a special separator character and don't pad with spaces, replacing
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all occurrences of this separator in symbol names (and other output)
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with a '.' character, that thus it's the only non valid separator.
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-v::
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--verbose::
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Be verbose, for instance, show the raw counts in addition to the
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diff.
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-q::
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--quiet::
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Do not show any message. (Suppress -v)
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-f::
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--force::
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Don't do ownership validation.
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--symfs=<directory>::
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Look for files with symbols relative to this directory.
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-b::
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--baseline-only::
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Show only items with match in baseline.
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-c::
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--compute::
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Differential computation selection - delta, ratio, wdiff, cycles,
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delta-abs (default is delta-abs). Default can be changed using
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diff.compute config option. See COMPARISON METHODS section for
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more info.
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--cycles-hist::
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Report a histogram and the standard deviation for cycles data.
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It can help us to judge if the reported cycles data is noisy or
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not. This option should be used with '-c cycles'.
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-p::
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--period::
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Show period values for both compared hist entries.
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-F::
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--formula::
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Show formula for given computation.
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-o::
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--order::
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Specify compute sorting column number. 0 means sorting by baseline
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overhead and 1 (default) means sorting by computed value of column 1
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(data from the first file other base baseline). Values more than 1
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can be used only if enough data files are provided.
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The default value can be set using the diff.order config option.
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--percentage::
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Determine how to display the overhead percentage of filtered entries.
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Filters can be applied by --comms, --dsos and/or --symbols options.
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"relative" means it's relative to filtered entries only so that the
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sum of shown entries will be always 100%. "absolute" means it retains
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the original value before and after the filter is applied.
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--time::
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Analyze samples within given time window. It supports time
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percent with multiple time ranges. Time string is 'a%/n,b%/m,...'
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or 'a%-b%,c%-%d,...'.
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For example:
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Select the second 10% time slice to diff:
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perf diff --time 10%/2
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Select from 0% to 10% time slice to diff:
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perf diff --time 0%-10%
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Select the first and the second 10% time slices to diff:
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perf diff --time 10%/1,10%/2
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Select from 0% to 10% and 30% to 40% slices to diff:
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perf diff --time 0%-10%,30%-40%
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It also supports analyzing samples within a given time window
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<start>,<stop>. Times have the format seconds.nanoseconds. If 'start'
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is not given (i.e. time string is ',x.y') then analysis starts at
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the beginning of the file. If stop time is not given (i.e. time
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string is 'x.y,') then analysis goes to the end of the file.
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Multiple ranges can be separated by spaces, which requires the argument
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to be quoted e.g. --time "1234.567,1234.789 1235,"
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Time string is'a1.b1,c1.d1:a2.b2,c2.d2'. Use ':' to separate timestamps
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for different perf.data files.
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For example, we get the timestamp information from 'perf script'.
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perf script -i perf.data.old
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mgen 13940 [000] 3946.361400: ...
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perf script -i perf.data
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mgen 13940 [000] 3971.150589 ...
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perf diff --time 3946.361400,:3971.150589,
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It analyzes the perf.data.old from the timestamp 3946.361400 to
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the end of perf.data.old and analyzes the perf.data from the
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timestamp 3971.150589 to the end of perf.data.
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--cpu:: Only diff samples for the list of CPUs provided. Multiple CPUs can
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be provided as a comma-separated list with no space: 0,1. Ranges of
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CPUs are specified with -: 0-2. Default is to report samples on all
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CPUs.
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--pid=::
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Only diff samples for given process ID (comma separated list).
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--tid=::
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Only diff samples for given thread ID (comma separated list).
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--stream::
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Enable hot streams comparison. Stream can be a callchain which is
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aggregated by the branch records from samples.
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COMPARISON
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----------
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The comparison is governed by the baseline file. The baseline perf.data
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file is iterated for samples. All other perf.data files specified on
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the command line are searched for the baseline sample pair. If the pair
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is found, specified computation is made and result is displayed.
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All samples from non-baseline perf.data files, that do not match any
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baseline entry, are displayed with empty space within baseline column
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and possible computation results (delta) in their related column.
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Example files samples:
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- file A with samples f1, f2, f3, f4, f6
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- file B with samples f2, f4, f5
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- file C with samples f1, f2, f5
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Example output:
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x - computation takes place for pair
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b - baseline sample percentage
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- perf diff A B C
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baseline/A compute/B compute/C samples
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---------------------------------------
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b x f1
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b x x f2
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b f3
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b x f4
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b f6
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x x f5
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- perf diff B A C
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baseline/B compute/A compute/C samples
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---------------------------------------
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b x x f2
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b x f4
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b x f5
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x x f1
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x f3
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x f6
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- perf diff C B A
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baseline/C compute/B compute/A samples
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---------------------------------------
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b x f1
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b x x f2
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b x f5
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x f3
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x x f4
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x f6
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COMPARISON METHODS
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------------------
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delta
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~~~~~
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If specified the 'Delta' column is displayed with value 'd' computed as:
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d = A->period_percent - B->period_percent
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with:
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- A/B being matching hist entry from data/baseline file specified
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(or perf.data/perf.data.old) respectively.
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- period_percent being the % of the hist entry period value within
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single data file
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- with filtering by -C, -d and/or -S, period_percent might be changed
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relative to how entries are filtered. Use --percentage=absolute to
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prevent such fluctuation.
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delta-abs
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~~~~~~~~~
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Same as 'delta` method, but sort the result with the absolute values.
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ratio
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~~~~~
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If specified the 'Ratio' column is displayed with value 'r' computed as:
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r = A->period / B->period
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with:
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- A/B being matching hist entry from data/baseline file specified
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(or perf.data/perf.data.old) respectively.
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- period being the hist entry period value
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wdiff:WEIGHT-B,WEIGHT-A
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~~~~~~~~~~~~~~~~~~~~~~~
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If specified the 'Weighted diff' column is displayed with value 'd' computed as:
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d = B->period * WEIGHT-A - A->period * WEIGHT-B
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- A/B being matching hist entry from data/baseline file specified
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(or perf.data/perf.data.old) respectively.
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- period being the hist entry period value
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- WEIGHT-A/WEIGHT-B being user supplied weights in the the '-c' option
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behind ':' separator like '-c wdiff:1,2'.
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- WEIGHT-A being the weight of the data file
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- WEIGHT-B being the weight of the baseline data file
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cycles
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~~~~~~
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If specified the '[Program Block Range] Cycles Diff' column is displayed.
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It displays the cycles difference of same program basic block amongst
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two perf.data. The program basic block is the code between two branches.
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'[Program Block Range]' indicates the range of a program basic block.
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Source line is reported if it can be found otherwise uses symbol+offset
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instead.
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SEE ALSO
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--------
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linkperf:perf-record[1], linkperf:perf-report[1]
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