1perf-diff(1)
2============
3
4NAME
5----
6perf-diff - Read perf.data files and display the differential profile
7
8SYNOPSIS
9--------
10[verse]
11'perf diff' [baseline file] [data file1] [[data file2] ... ]
12
13DESCRIPTION
14-----------
15This command displays the performance difference amongst two or more perf.data
16files captured via perf record.
17
18If no parameters are passed it will assume perf.data.old and perf.data.
19
20The differential profile is displayed only for events matching both
21specified perf.data files.
22
23If no parameters are passed the samples will be sorted by dso and symbol.
24As the perf.data files could come from different binaries, the symbols addresses
25could vary. So perf diff is based on the comparison of the files and
26symbols name.
27
28OPTIONS
29-------
30-D::
31--dump-raw-trace::
32        Dump raw trace in ASCII.
33
34--kallsyms=<file>::
35        kallsyms pathname
36
37-m::
38--modules::
39        Load module symbols. WARNING: use only with -k and LIVE kernel
40
41-d::
42--dsos=::
43	Only consider symbols in these dsos. CSV that understands
44	file://filename entries.  This option will affect the percentage
45	of the Baseline/Delta column.  See --percentage for more info.
46
47-C::
48--comms=::
49	Only consider symbols in these comms. CSV that understands
50	file://filename entries.  This option will affect the percentage
51	of the Baseline/Delta column.  See --percentage for more info.
52
53-S::
54--symbols=::
55	Only consider these symbols. CSV that understands
56	file://filename entries.  This option will affect the percentage
57	of the Baseline/Delta column.  See --percentage for more info.
58
59-s::
60--sort=::
61	Sort by key(s): pid, comm, dso, symbol, cpu, parent, srcline.
62	Please see description of --sort in the perf-report man page.
63
64-t::
65--field-separator=::
66
67	Use a special separator character and don't pad with spaces, replacing
68	all occurrences of this separator in symbol names (and other output)
69	with a '.' character, that thus it's the only non valid separator.
70
71-v::
72--verbose::
73	Be verbose, for instance, show the raw counts in addition to the
74	diff.
75
76-f::
77--force::
78       Don't complain, do it.
79
80--symfs=<directory>::
81        Look for files with symbols relative to this directory.
82
83-b::
84--baseline-only::
85        Show only items with match in baseline.
86
87-c::
88--compute::
89        Differential computation selection - delta,ratio,wdiff (default is delta).
90        See COMPARISON METHODS section for more info.
91
92-p::
93--period::
94        Show period values for both compared hist entries.
95
96-F::
97--formula::
98        Show formula for given computation.
99
100-o::
101--order::
102       Specify compute sorting column number.
103
104--percentage::
105	Determine how to display the overhead percentage of filtered entries.
106	Filters can be applied by --comms, --dsos and/or --symbols options.
107
108	"relative" means it's relative to filtered entries only so that the
109	sum of shown entries will be always 100%.  "absolute" means it retains
110	the original value before and after the filter is applied.
111
112COMPARISON
113----------
114The comparison is governed by the baseline file. The baseline perf.data
115file is iterated for samples. All other perf.data files specified on
116the command line are searched for the baseline sample pair. If the pair
117is found, specified computation is made and result is displayed.
118
119All samples from non-baseline perf.data files, that do not match any
120baseline entry, are displayed with empty space within baseline column
121and possible computation results (delta) in their related column.
122
123Example files samples:
124- file A with samples f1, f2, f3, f4,    f6
125- file B with samples     f2,     f4, f5
126- file C with samples f1, f2,         f5
127
128Example output:
129  x - computation takes place for pair
130  b - baseline sample percentage
131
132- perf diff A B C
133
134  baseline/A compute/B compute/C  samples
135  ---------------------------------------
136  b                    x          f1
137  b          x         x          f2
138  b                               f3
139  b          x                    f4
140  b                               f6
141             x         x          f5
142
143- perf diff B A C
144
145  baseline/B compute/A compute/C  samples
146  ---------------------------------------
147  b          x         x          f2
148  b          x                    f4
149  b                    x          f5
150             x         x          f1
151             x                    f3
152             x                    f6
153
154- perf diff C B A
155
156  baseline/C compute/B compute/A  samples
157  ---------------------------------------
158  b                    x          f1
159  b          x         x          f2
160  b          x                    f5
161                       x          f3
162             x         x          f4
163                       x          f6
164
165COMPARISON METHODS
166------------------
167delta
168~~~~~
169If specified the 'Delta' column is displayed with value 'd' computed as:
170
171  d = A->period_percent - B->period_percent
172
173with:
174  - A/B being matching hist entry from data/baseline file specified
175    (or perf.data/perf.data.old) respectively.
176
177  - period_percent being the % of the hist entry period value within
178    single data file
179
180  - with filtering by -C, -d and/or -S, period_percent might be changed
181    relative to how entries are filtered.  Use --percentage=absolute to
182    prevent such fluctuation.
183
184ratio
185~~~~~
186If specified the 'Ratio' column is displayed with value 'r' computed as:
187
188  r = A->period / B->period
189
190with:
191  - A/B being matching hist entry from data/baseline file specified
192    (or perf.data/perf.data.old) respectively.
193
194  - period being the hist entry period value
195
196wdiff:WEIGHT-B,WEIGHT-A
197~~~~~~~~~~~~~~~~~~~~~~~
198If specified the 'Weighted diff' column is displayed with value 'd' computed as:
199
200   d = B->period * WEIGHT-A - A->period * WEIGHT-B
201
202  - A/B being matching hist entry from data/baseline file specified
203    (or perf.data/perf.data.old) respectively.
204
205  - period being the hist entry period value
206
207  - WEIGHT-A/WEIGHT-B being user supplied weights in the the '-c' option
208    behind ':' separator like '-c wdiff:1,2'.
209    - WEIGHT-A being the weight of the data file
210    - WEIGHT-B being the weight of the baseline data file
211
212SEE ALSO
213--------
214linkperf:perf-record[1], linkperf:perf-report[1]
215