1 2 ------------------------------ 3 ****** perf by examples ****** 4 ------------------------------ 5 6 [ From an e-mail by Ingo Molnar, https://lore.kernel.org/lkml/20090804195717.GA5998@elte.hu ] 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
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