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Subjectperf: "Longum est iter per praecepta, breve et efficax per exempla"

A few examples of how 'perf' can be used, from an e-mail by
Ingo Molnar http://lkml.org/lkml/2009/8/4/346.

Signed-off-by: Carlos R. Mafra <crmafra2@gmail.com>
---
This "patch" is my way of _suggesting_ some "documentation by examples"
of what 'perf' can do to the guys who can really write it :-)


tools/perf/Documentation/perf-examples.txt | 225 ++++++++++++++++++++++++++++
1 files changed, 225 insertions(+), 0 deletions(-)
create mode 100644 tools/perf/Documentation/perf-examples.txt
diff --git a/tools/perf/Documentation/perf-examples.txt b/tools/perf/Documentation/perf-examples.txt
new file mode 100644
index 0000000..d7a861d
--- /dev/null
+++ b/tools/perf/Documentation/perf-examples.txt
@@ -0,0 +1,225 @@
+
+ ------------------------------
+ ****** 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_direct [Tracepoint event]
+ kmem:mm_pagevec_free [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_pagevec_free -e kmem:mm_page_free_direct ./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_pagevec_free
+ 20934 kmem:mm_page_free_direct
+
+ 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_pagevec_free -e
+ kmem:mm_page_free_direct ./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_pagevec_free ( +- 0.934% )
+ 18376 kmem:mm_page_free_direct ( +- 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 -f -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 -f -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_pagevec_free -e
+kmem:mm_page_free_direct sleep 10
+
+ Performance counter stats for 'sleep 10':
+
+ 171585 kmem:mm_page_pcpu_drain
+ 322114 kmem:mm_page_alloc
+ 73623 kmem:mm_pagevec_free
+ 254115 kmem:mm_page_free_direct
+
+ 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_pagevec_free -e
+ kmem:mm_page_free_direct 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_pagevec_free ( +- 4.820% )
+ 25653 kmem:mm_page_free_direct ( +- 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
+
+
--
1.6.4.rc1.13.gec7b




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