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diff --git a/tools/perf/Documentation/perf-diff.txt b/tools/perf/Documentation/perf-diff.txt new file mode 100644 index 000000000..be65bd55a --- /dev/null +++ b/tools/perf/Documentation/perf-diff.txt @@ -0,0 +1,305 @@ +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 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, 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] |