GNU Linux-libre 4.19.211-gnu1
[releases.git] / tools / perf / Documentation / examples.txt
1
2                 ------------------------------
3                 ****** perf by examples ******
4                 ------------------------------
5
6 [ From an e-mail by Ingo Molnar, http://lkml.org/lkml/2009/8/4/346 ]
7
8
9 First, discovery/enumeration of available counters can be done via
10 'perf list':
11
12 titan:~> perf list
13   [...]
14   kmem:kmalloc                             [Tracepoint event]
15   kmem:kmem_cache_alloc                    [Tracepoint event]
16   kmem:kmalloc_node                        [Tracepoint event]
17   kmem:kmem_cache_alloc_node               [Tracepoint event]
18   kmem:kfree                               [Tracepoint event]
19   kmem:kmem_cache_free                     [Tracepoint event]
20   kmem:mm_page_free                        [Tracepoint event]
21   kmem:mm_page_free_batched                [Tracepoint event]
22   kmem:mm_page_alloc                       [Tracepoint event]
23   kmem:mm_page_alloc_zone_locked           [Tracepoint event]
24   kmem:mm_page_pcpu_drain                  [Tracepoint event]
25   kmem:mm_page_alloc_extfrag               [Tracepoint event]
26
27 Then any (or all) of the above event sources can be activated and
28 measured. For example the page alloc/free properties of a 'hackbench
29 run' are:
30
31  titan:~> perf stat -e kmem:mm_page_pcpu_drain -e kmem:mm_page_alloc
32  -e kmem:mm_page_free_batched -e kmem:mm_page_free ./hackbench 10
33  Time: 0.575
34
35  Performance counter stats for './hackbench 10':
36
37           13857  kmem:mm_page_pcpu_drain
38           27576  kmem:mm_page_alloc
39            6025  kmem:mm_page_free_batched
40           20934  kmem:mm_page_free
41
42     0.613972165  seconds time elapsed
43
44 You can observe the statistical properties as well, by using the
45 'repeat the workload N times' feature of perf stat:
46
47  titan:~> perf stat --repeat 5 -e kmem:mm_page_pcpu_drain -e
48    kmem:mm_page_alloc -e kmem:mm_page_free_batched -e
49    kmem:mm_page_free ./hackbench 10
50  Time: 0.627
51  Time: 0.644
52  Time: 0.564
53  Time: 0.559
54  Time: 0.626
55
56  Performance counter stats for './hackbench 10' (5 runs):
57
58           12920  kmem:mm_page_pcpu_drain    ( +-   3.359% )
59           25035  kmem:mm_page_alloc         ( +-   3.783% )
60            6104  kmem:mm_page_free_batched  ( +-   0.934% )
61           18376  kmem:mm_page_free          ( +-   4.941% )
62
63     0.643954516  seconds time elapsed   ( +-   2.363% )
64
65 Furthermore, these tracepoints can be used to sample the workload as
66 well. For example the page allocations done by a 'git gc' can be
67 captured the following way:
68
69  titan:~/git> perf record -e kmem:mm_page_alloc -c 1 ./git gc
70  Counting objects: 1148, done.
71  Delta compression using up to 2 threads.
72  Compressing objects: 100% (450/450), done.
73  Writing objects: 100% (1148/1148), done.
74  Total 1148 (delta 690), reused 1148 (delta 690)
75  [ perf record: Captured and wrote 0.267 MB perf.data (~11679 samples) ]
76
77 To check which functions generated page allocations:
78
79  titan:~/git> perf report
80  # Samples: 10646
81  #
82  # Overhead          Command               Shared Object
83  # ........  ...............  ..........................
84  #
85     23.57%       git-repack  /lib64/libc-2.5.so
86     21.81%              git  /lib64/libc-2.5.so
87     14.59%              git  ./git
88     11.79%       git-repack  ./git
89      7.12%              git  /lib64/ld-2.5.so
90      3.16%       git-repack  /lib64/libpthread-2.5.so
91      2.09%       git-repack  /bin/bash
92      1.97%               rm  /lib64/libc-2.5.so
93      1.39%               mv  /lib64/ld-2.5.so
94      1.37%               mv  /lib64/libc-2.5.so
95      1.12%       git-repack  /lib64/ld-2.5.so
96      0.95%               rm  /lib64/ld-2.5.so
97      0.90%  git-update-serv  /lib64/libc-2.5.so
98      0.73%  git-update-serv  /lib64/ld-2.5.so
99      0.68%             perf  /lib64/libpthread-2.5.so
100      0.64%       git-repack  /usr/lib64/libz.so.1.2.3
101
102 Or to see it on a more finegrained level:
103
104 titan:~/git> perf report --sort comm,dso,symbol
105 # Samples: 10646
106 #
107 # Overhead          Command               Shared Object  Symbol
108 # ........  ...............  ..........................  ......
109 #
110      9.35%       git-repack  ./git                       [.] insert_obj_hash
111      9.12%              git  ./git                       [.] insert_obj_hash
112      7.31%              git  /lib64/libc-2.5.so          [.] memcpy
113      6.34%       git-repack  /lib64/libc-2.5.so          [.] _int_malloc
114      6.24%       git-repack  /lib64/libc-2.5.so          [.] memcpy
115      5.82%       git-repack  /lib64/libc-2.5.so          [.] __GI___fork
116      5.47%              git  /lib64/libc-2.5.so          [.] _int_malloc
117      2.99%              git  /lib64/libc-2.5.so          [.] memset
118
119 Furthermore, call-graph sampling can be done too, of page
120 allocations - to see precisely what kind of page allocations there
121 are:
122
123  titan:~/git> perf record -g -e kmem:mm_page_alloc -c 1 ./git gc
124  Counting objects: 1148, done.
125  Delta compression using up to 2 threads.
126  Compressing objects: 100% (450/450), done.
127  Writing objects: 100% (1148/1148), done.
128  Total 1148 (delta 690), reused 1148 (delta 690)
129  [ perf record: Captured and wrote 0.963 MB perf.data (~42069 samples) ]
130
131  titan:~/git> perf report -g
132  # Samples: 10686
133  #
134  # Overhead          Command               Shared Object
135  # ........  ...............  ..........................
136  #
137     23.25%       git-repack  /lib64/libc-2.5.so
138                 |
139                 |--50.00%-- _int_free
140                 |
141                 |--37.50%-- __GI___fork
142                 |          make_child
143                 |
144                 |--12.50%-- ptmalloc_unlock_all2
145                 |          make_child
146                 |
147                  --6.25%-- __GI_strcpy
148     21.61%              git  /lib64/libc-2.5.so
149                 |
150                 |--30.00%-- __GI_read
151                 |          |
152                 |           --83.33%-- git_config_from_file
153                 |                     git_config
154                 |                     |
155    [...]
156
157 Or you can observe the whole system's page allocations for 10
158 seconds:
159
160 titan:~/git> perf stat -a -e kmem:mm_page_pcpu_drain -e
161 kmem:mm_page_alloc -e kmem:mm_page_free_batched -e
162 kmem:mm_page_free sleep 10
163
164  Performance counter stats for 'sleep 10':
165
166          171585  kmem:mm_page_pcpu_drain
167          322114  kmem:mm_page_alloc
168           73623  kmem:mm_page_free_batched
169          254115  kmem:mm_page_free
170
171    10.000591410  seconds time elapsed
172
173 Or observe how fluctuating the page allocations are, via statistical
174 analysis done over ten 1-second intervals:
175
176  titan:~/git> perf stat --repeat 10 -a -e kmem:mm_page_pcpu_drain -e
177    kmem:mm_page_alloc -e kmem:mm_page_free_batched -e
178    kmem:mm_page_free sleep 1
179
180  Performance counter stats for 'sleep 1' (10 runs):
181
182           17254  kmem:mm_page_pcpu_drain    ( +-   3.709% )
183           34394  kmem:mm_page_alloc         ( +-   4.617% )
184            7509  kmem:mm_page_free_batched  ( +-   4.820% )
185           25653  kmem:mm_page_free          ( +-   3.672% )
186
187     1.058135029  seconds time elapsed   ( +-   3.089% )
188
189 Or you can annotate the recorded 'git gc' run on a per symbol basis
190 and check which instructions/source-code generated page allocations:
191
192  titan:~/git> perf annotate __GI___fork
193  ------------------------------------------------
194   Percent |      Source code & Disassembly of libc-2.5.so
195  ------------------------------------------------
196           :
197           :
198           :      Disassembly of section .plt:
199           :      Disassembly of section .text:
200           :
201           :      00000031a2e95560 <__fork>:
202  [...]
203      0.00 :        31a2e95602:   b8 38 00 00 00          mov    $0x38,%eax
204      0.00 :        31a2e95607:   0f 05                   syscall
205     83.42 :        31a2e95609:   48 3d 00 f0 ff ff       cmp    $0xfffffffffffff000,%rax
206      0.00 :        31a2e9560f:   0f 87 4d 01 00 00       ja     31a2e95762 <__fork+0x202>
207      0.00 :        31a2e95615:   85 c0                   test   %eax,%eax
208
209 ( this shows that 83.42% of __GI___fork's page allocations come from
210   the 0x38 system call it performs. )
211
212 etc. etc. - a lot more is possible. I could list a dozen of
213 other different usecases straight away - neither of which is
214 possible via /proc/vmstat.
215
216 /proc/vmstat is not in the same league really, in terms of
217 expressive power of system analysis and performance
218 analysis.
219
220 All that the above results needed were those new tracepoints
221 in include/tracing/events/kmem.h.
222
223         Ingo
224
225