perf: "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> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Valdis.Kletnieks@vt.edu LKML-Reference: <20090805185334.GA4535@Pilar.aei.mpg.de> Signed-off-by: Ingo Molnar <mingo@elte.hu>
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Carlos R. Mafra
Ingo Molnar
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tools/perf/Documentation/perf-examples.txt
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tools/perf/Documentation/perf-examples.txt
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------------------------------
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****** perf by examples ******
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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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First, discovery/enumeration of available counters can be done via
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'perf list':
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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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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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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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Performance counter stats for './hackbench 10':
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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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0.613972165 seconds time elapsed
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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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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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Performance counter stats for './hackbench 10' (5 runs):
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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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0.643954516 seconds time elapsed ( +- 2.363% )
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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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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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To check which functions generated page allocations:
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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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Or to see it on a more finegrained level:
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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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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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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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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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|--50.00%-- _int_free
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|--37.50%-- __GI___fork
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| make_child
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|--12.50%-- ptmalloc_unlock_all2
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| make_child
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--6.25%-- __GI_strcpy
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21.61% git /lib64/libc-2.5.so
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|--30.00%-- __GI_read
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| --83.33%-- git_config_from_file
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| git_config
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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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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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Performance counter stats for 'sleep 10':
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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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10.000591410 seconds time elapsed
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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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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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Performance counter stats for 'sleep 1' (10 runs):
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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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1.058135029 seconds time elapsed ( +- 3.089% )
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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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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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( 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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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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/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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All that the above results needed were those new tracepoints
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in include/tracing/events/kmem.h.
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Ingo
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