| ------------------------------ | |
| ****** perf by examples ****** | |
| ------------------------------ | |
| [ From an e-mail by Ingo Molnar, http://lkml.org/lkml/2009/8/4/346 ] | |
| First, discovery/enumeration of available counters can be done via | |
| 'perf list': | |
| titan:~> perf list | |
| [...] | |
| kmem:kmalloc [Tracepoint event] | |
| kmem:kmem_cache_alloc [Tracepoint event] | |
| kmem:kmalloc_node [Tracepoint event] | |
| kmem:kmem_cache_alloc_node [Tracepoint event] | |
| kmem:kfree [Tracepoint event] | |
| kmem:kmem_cache_free [Tracepoint event] | |
| kmem:mm_page_free [Tracepoint event] | |
| kmem:mm_page_free_batched [Tracepoint event] | |
| kmem:mm_page_alloc [Tracepoint event] | |
| kmem:mm_page_alloc_zone_locked [Tracepoint event] | |
| kmem:mm_page_pcpu_drain [Tracepoint event] | |
| kmem:mm_page_alloc_extfrag [Tracepoint event] | |
| Then any (or all) of the above event sources can be activated and | |
| measured. For example the page alloc/free properties of a 'hackbench | |
| run' are: | |
| titan:~> perf stat -e kmem:mm_page_pcpu_drain -e kmem:mm_page_alloc | |
| -e kmem:mm_page_free_batched -e kmem:mm_page_free ./hackbench 10 | |
| Time: 0.575 | |
| Performance counter stats for './hackbench 10': | |
| 13857 kmem:mm_page_pcpu_drain | |
| 27576 kmem:mm_page_alloc | |
| 6025 kmem:mm_page_free_batched | |
| 20934 kmem:mm_page_free | |
| 0.613972165 seconds time elapsed | |
| You can observe the statistical properties as well, by using the | |
| 'repeat the workload N times' feature of perf stat: | |
| titan:~> perf stat --repeat 5 -e kmem:mm_page_pcpu_drain -e | |
| kmem:mm_page_alloc -e kmem:mm_page_free_batched -e | |
| kmem:mm_page_free ./hackbench 10 | |
| Time: 0.627 | |
| Time: 0.644 | |
| Time: 0.564 | |
| Time: 0.559 | |
| Time: 0.626 | |
| Performance counter stats for './hackbench 10' (5 runs): | |
| 12920 kmem:mm_page_pcpu_drain ( +- 3.359% ) | |
| 25035 kmem:mm_page_alloc ( +- 3.783% ) | |
| 6104 kmem:mm_page_free_batched ( +- 0.934% ) | |
| 18376 kmem:mm_page_free ( +- 4.941% ) | |
| 0.643954516 seconds time elapsed ( +- 2.363% ) | |
| Furthermore, these tracepoints can be used to sample the workload as | |
| well. For example the page allocations done by a 'git gc' can be | |
| captured the following way: | |
| titan:~/git> perf record -e kmem:mm_page_alloc -c 1 ./git gc | |
| Counting objects: 1148, done. | |
| Delta compression using up to 2 threads. | |
| Compressing objects: 100% (450/450), done. | |
| Writing objects: 100% (1148/1148), done. | |
| Total 1148 (delta 690), reused 1148 (delta 690) | |
| [ perf record: Captured and wrote 0.267 MB perf.data (~11679 samples) ] | |
| To check which functions generated page allocations: | |
| titan:~/git> perf report | |
| # Samples: 10646 | |
| # | |
| # Overhead Command Shared Object | |
| # ........ ............... .......................... | |
| # | |
| 23.57% git-repack /lib64/libc-2.5.so | |
| 21.81% git /lib64/libc-2.5.so | |
| 14.59% git ./git | |
| 11.79% git-repack ./git | |
| 7.12% git /lib64/ld-2.5.so | |
| 3.16% git-repack /lib64/libpthread-2.5.so | |
| 2.09% git-repack /bin/bash | |
| 1.97% rm /lib64/libc-2.5.so | |
| 1.39% mv /lib64/ld-2.5.so | |
| 1.37% mv /lib64/libc-2.5.so | |
| 1.12% git-repack /lib64/ld-2.5.so | |
| 0.95% rm /lib64/ld-2.5.so | |
| 0.90% git-update-serv /lib64/libc-2.5.so | |
| 0.73% git-update-serv /lib64/ld-2.5.so | |
| 0.68% perf /lib64/libpthread-2.5.so | |
| 0.64% git-repack /usr/lib64/libz.so.1.2.3 | |
| Or to see it on a more finegrained level: | |
| titan:~/git> perf report --sort comm,dso,symbol | |
| # Samples: 10646 | |
| # | |
| # Overhead Command Shared Object Symbol | |
| # ........ ............... .......................... ...... | |
| # | |
| 9.35% git-repack ./git [.] insert_obj_hash | |
| 9.12% git ./git [.] insert_obj_hash | |
| 7.31% git /lib64/libc-2.5.so [.] memcpy | |
| 6.34% git-repack /lib64/libc-2.5.so [.] _int_malloc | |
| 6.24% git-repack /lib64/libc-2.5.so [.] memcpy | |
| 5.82% git-repack /lib64/libc-2.5.so [.] __GI___fork | |
| 5.47% git /lib64/libc-2.5.so [.] _int_malloc | |
| 2.99% git /lib64/libc-2.5.so [.] memset | |
| Furthermore, call-graph sampling can be done too, of page | |
| allocations - to see precisely what kind of page allocations there | |
| are: | |
| titan:~/git> perf record -g -e kmem:mm_page_alloc -c 1 ./git gc | |
| Counting objects: 1148, done. | |
| Delta compression using up to 2 threads. | |
| Compressing objects: 100% (450/450), done. | |
| Writing objects: 100% (1148/1148), done. | |
| Total 1148 (delta 690), reused 1148 (delta 690) | |
| [ perf record: Captured and wrote 0.963 MB perf.data (~42069 samples) ] | |
| titan:~/git> perf report -g | |
| # Samples: 10686 | |
| # | |
| # Overhead Command Shared Object | |
| # ........ ............... .......................... | |
| # | |
| 23.25% git-repack /lib64/libc-2.5.so | |
| | | |
| |--50.00%-- _int_free | |
| | | |
| |--37.50%-- __GI___fork | |
| | make_child | |
| | | |
| |--12.50%-- ptmalloc_unlock_all2 | |
| | make_child | |
| | | |
| --6.25%-- __GI_strcpy | |
| 21.61% git /lib64/libc-2.5.so | |
| | | |
| |--30.00%-- __GI_read | |
| | | | |
| | --83.33%-- git_config_from_file | |
| | git_config | |
| | | | |
| [...] | |
| Or you can observe the whole system's page allocations for 10 | |
| seconds: | |
| titan:~/git> perf stat -a -e kmem:mm_page_pcpu_drain -e | |
| kmem:mm_page_alloc -e kmem:mm_page_free_batched -e | |
| kmem:mm_page_free sleep 10 | |
| Performance counter stats for 'sleep 10': | |
| 171585 kmem:mm_page_pcpu_drain | |
| 322114 kmem:mm_page_alloc | |
| 73623 kmem:mm_page_free_batched | |
| 254115 kmem:mm_page_free | |
| 10.000591410 seconds time elapsed | |
| Or observe how fluctuating the page allocations are, via statistical | |
| analysis done over ten 1-second intervals: | |
| titan:~/git> perf stat --repeat 10 -a -e kmem:mm_page_pcpu_drain -e | |
| kmem:mm_page_alloc -e kmem:mm_page_free_batched -e | |
| kmem:mm_page_free sleep 1 | |
| Performance counter stats for 'sleep 1' (10 runs): | |
| 17254 kmem:mm_page_pcpu_drain ( +- 3.709% ) | |
| 34394 kmem:mm_page_alloc ( +- 4.617% ) | |
| 7509 kmem:mm_page_free_batched ( +- 4.820% ) | |
| 25653 kmem:mm_page_free ( +- 3.672% ) | |
| 1.058135029 seconds time elapsed ( +- 3.089% ) | |
| Or you can annotate the recorded 'git gc' run on a per symbol basis | |
| and check which instructions/source-code generated page allocations: | |
| titan:~/git> perf annotate __GI___fork | |
| ------------------------------------------------ | |
| Percent | Source code & Disassembly of libc-2.5.so | |
| ------------------------------------------------ | |
| : | |
| : | |
| : Disassembly of section .plt: | |
| : Disassembly of section .text: | |
| : | |
| : 00000031a2e95560 <__fork>: | |
| [...] | |
| 0.00 : 31a2e95602: b8 38 00 00 00 mov $0x38,%eax | |
| 0.00 : 31a2e95607: 0f 05 syscall | |
| 83.42 : 31a2e95609: 48 3d 00 f0 ff ff cmp $0xfffffffffffff000,%rax | |
| 0.00 : 31a2e9560f: 0f 87 4d 01 00 00 ja 31a2e95762 <__fork+0x202> | |
| 0.00 : 31a2e95615: 85 c0 test %eax,%eax | |
| ( this shows that 83.42% of __GI___fork's page allocations come from | |
| the 0x38 system call it performs. ) | |
| etc. etc. - a lot more is possible. I could list a dozen of | |
| other different usecases straight away - neither of which is | |
| possible via /proc/vmstat. | |
| /proc/vmstat is not in the same league really, in terms of | |
| expressive power of system analysis and performance | |
| analysis. | |
| All that the above results needed were those new tracepoints | |
| in include/tracing/events/kmem.h. | |
| Ingo | |