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