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-q::
77--quiet::
78	Do not show any message.  (Suppress -v)
79
80-f::
81--force::
82        Don't do ownership validation.
83
84--symfs=<directory>::
85        Look for files with symbols relative to this directory.
86
87-b::
88--baseline-only::
89        Show only items with match in baseline.
90
91-c::
92--compute::
93        Differential computation selection - delta, ratio, wdiff, delta-abs
94        (default is delta-abs).  Default can be changed using diff.compute
95        config option.  See COMPARISON METHODS section for more info.
96
97-p::
98--period::
99        Show period values for both compared hist entries.
100
101-F::
102--formula::
103        Show formula for given computation.
104
105-o::
106--order::
107       Specify compute sorting column number.  0 means sorting by baseline
108       overhead and 1 (default) means sorting by computed value of column 1
109       (data from the first file other base baseline).  Values more than 1
110       can be used only if enough data files are provided.
111       The default value can be set using the diff.order config option.
112
113--percentage::
114	Determine how to display the overhead percentage of filtered entries.
115	Filters can be applied by --comms, --dsos and/or --symbols options.
116
117	"relative" means it's relative to filtered entries only so that the
118	sum of shown entries will be always 100%.  "absolute" means it retains
119	the original value before and after the filter is applied.
120
121COMPARISON
122----------
123The comparison is governed by the baseline file. The baseline perf.data
124file is iterated for samples. All other perf.data files specified on
125the command line are searched for the baseline sample pair. If the pair
126is found, specified computation is made and result is displayed.
127
128All samples from non-baseline perf.data files, that do not match any
129baseline entry, are displayed with empty space within baseline column
130and possible computation results (delta) in their related column.
131
132Example files samples:
133- file A with samples f1, f2, f3, f4,    f6
134- file B with samples     f2,     f4, f5
135- file C with samples f1, f2,         f5
136
137Example output:
138  x - computation takes place for pair
139  b - baseline sample percentage
140
141- perf diff A B C
142
143  baseline/A compute/B compute/C  samples
144  ---------------------------------------
145  b                    x          f1
146  b          x         x          f2
147  b                               f3
148  b          x                    f4
149  b                               f6
150             x         x          f5
151
152- perf diff B A C
153
154  baseline/B compute/A compute/C  samples
155  ---------------------------------------
156  b          x         x          f2
157  b          x                    f4
158  b                    x          f5
159             x         x          f1
160             x                    f3
161             x                    f6
162
163- perf diff C B A
164
165  baseline/C compute/B compute/A  samples
166  ---------------------------------------
167  b                    x          f1
168  b          x         x          f2
169  b          x                    f5
170                       x          f3
171             x         x          f4
172                       x          f6
173
174COMPARISON METHODS
175------------------
176delta
177~~~~~
178If specified the 'Delta' column is displayed with value 'd' computed as:
179
180  d = A->period_percent - B->period_percent
181
182with:
183  - A/B being matching hist entry from data/baseline file specified
184    (or perf.data/perf.data.old) respectively.
185
186  - period_percent being the % of the hist entry period value within
187    single data file
188
189  - with filtering by -C, -d and/or -S, period_percent might be changed
190    relative to how entries are filtered.  Use --percentage=absolute to
191    prevent such fluctuation.
192
193delta-abs
194~~~~~~~~~
195Same as 'delta` method, but sort the result with the absolute values.
196
197ratio
198~~~~~
199If specified the 'Ratio' column is displayed with value 'r' computed as:
200
201  r = A->period / B->period
202
203with:
204  - A/B being matching hist entry from data/baseline file specified
205    (or perf.data/perf.data.old) respectively.
206
207  - period being the hist entry period value
208
209wdiff:WEIGHT-B,WEIGHT-A
210~~~~~~~~~~~~~~~~~~~~~~~
211If specified the 'Weighted diff' column is displayed with value 'd' computed as:
212
213   d = B->period * WEIGHT-A - A->period * WEIGHT-B
214
215  - A/B being matching hist entry from data/baseline file specified
216    (or perf.data/perf.data.old) respectively.
217
218  - period being the hist entry period value
219
220  - WEIGHT-A/WEIGHT-B being user supplied weights in the the '-c' option
221    behind ':' separator like '-c wdiff:1,2'.
222    - WEIGHT-A being the weight of the data file
223    - WEIGHT-B being the weight of the baseline data file
224
225SEE ALSO
226--------
227linkperf:perf-record[1], linkperf:perf-report[1]
228