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