Re: [lkp] [mremap] 5d1904204c: will-it-scale.per_thread_ops -13.1% regression

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On Mon, Nov 28, 2016 at 02:21:53AM +0800, kernel test robot wrote:
> 
> Greeting,

Thanks for the report.

> 
> FYI, we noticed a -13.1% regression of will-it-scale.per_thread_ops due to commit:

I took a look at the test, it
1 creates an eventfd with the counter's initial value set to 0;
2 writes 1 to this eventfd, i.e. set its counter to 1;
3 does read, i.e. return the value of 1 and reset the counter to 0;
4 loop to step 2.

I don't see move_vma/move_page_tables/move_ptes involved in this test
though.

I also tried trace-cmd to see if I missed anything:
# trace-cmd record -p function --func-stack -l move_vma -l move_page_tables -l move_huge_pmd ./eventfd1_threads -t 1 -s 10

The report is:
# /usr/local/bin/trace-cmd report
CPU 0 is empty
CPU 1 is empty
CPU 2 is empty
CPU 3 is empty
CPU 4 is empty
CPU 5 is empty
CPU 6 is empty
cpus=8
 eventfd1_thread-21210 [007]  2626.438884: function:             move_page_tables
 eventfd1_thread-21210 [007]  2626.438889: kernel_stack:         <stack trace>
=> setup_arg_pages (ffffffff81282ac0)
=> load_elf_binary (ffffffff812e4503)
=> search_binary_handler (ffffffff81282268)
=> exec_binprm (ffffffff8149d6ab)
=> do_execveat_common.isra.41 (ffffffff81284882)
=> do_execve (ffffffff8128498c)
=> SyS_execve (ffffffff81284c3e)
=> do_syscall_64 (ffffffff81002a76)
=> return_from_SYSCALL_64 (ffffffff81cbd509)

i.e., only one call of move_page_tables is in the log, and it's at the
very beginning of the run, not during.

I also did the run on my Sandybridge desktop(4 cores 8 threads with 12G
memory) and a Broadwell EP, they don't have this performance drop
either. Perhaps this problem only occurs on some machine.

I'll continue to take a look at this report, hopefully I can figure out
why this commit is bisected while its change doesn't seem to play a part
in the test. Your comments are greatly appreciated.

Thanks,
Aaron

> 
> 
> commit 5d1904204c99596b50a700f092fe49d78edba400 ("mremap: fix race between mremap() and page cleanning")
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> 
> in testcase: will-it-scale
> on test machine: 12 threads Intel(R) Core(TM) i7 CPU X 980 @ 3.33GHz with 6G memory
> with following parameters:
> 
> 	test: eventfd1
> 	cpufreq_governor: performance
> 
> test-description: Will It Scale takes a testcase and runs it from 1 through to n parallel copies to see if the testcase will scale. It builds both a process and threads based test in order to see any differences between the two.
> test-url: https://github.com/antonblanchard/will-it-scale
> 
> 
> Details are as below:
> -------------------------------------------------------------------------------------------------->
> 
> 
> To reproduce:
> 
>         git clone git://git.kernel.org/pub/scm/linux/kernel/git/wfg/lkp-tests.git
>         cd lkp-tests
>         bin/lkp install job.yaml  # job file is attached in this email
>         bin/lkp run     job.yaml
> 
> =========================================================================================
> compiler/cpufreq_governor/kconfig/rootfs/tbox_group/test/testcase:
>   gcc-6/performance/x86_64-rhel-7.2/debian-x86_64-2016-08-31.cgz/wsm/eventfd1/will-it-scale
> 
> commit: 
>   961b708e95 (" fixes for amdgpu, and a bunch of arm drivers.")
>   5d1904204c ("mremap: fix race between mremap() and page cleanning")
> 
> 961b708e95181041 5d1904204c99596b50a700f092 
> ---------------- -------------------------- 
>        fail:runs  %reproduction    fail:runs
>            |             |             |    
>          %stddev     %change         %stddev
>              \          |                \  
>    2459656 ±  0%     -13.1%    2137017 ±  1%  will-it-scale.per_thread_ops
>    2865527 ±  3%      +4.2%    2986100 ±  0%  will-it-scale.per_process_ops
>       0.62 ± 11%     -13.2%       0.54 ±  1%  will-it-scale.scalability
>     893.40 ±  0%      +1.3%     905.24 ±  0%  will-it-scale.time.system_time
>     169.92 ±  0%      -7.0%     158.09 ±  0%  will-it-scale.time.user_time
>     176943 ±  6%     +26.1%     223131 ± 11%  cpuidle.C1E-NHM.time
>      10.00 ±  6%     -10.9%       8.91 ±  4%  turbostat.CPU%c6
>      30508 ±  1%      +3.4%      31541 ±  0%  vmstat.system.cs
>      27239 ±  0%      +1.5%      27650 ±  0%  vmstat.system.in
>       2.03 ±  2%     -11.6%       1.80 ±  6%  perf-profile.calltrace.cycles-pp.entry_SYSCALL_64
>       4.11 ±  1%     -12.0%       3.61 ±  4%  perf-profile.calltrace.cycles-pp.entry_SYSCALL_64_after_swapgs
>       1.70 ±  3%     -13.8%       1.46 ±  5%  perf-profile.children.cycles-pp.__fget_light
>       2.03 ±  2%     -11.6%       1.80 ±  6%  perf-profile.children.cycles-pp.entry_SYSCALL_64
>       4.11 ±  1%     -12.0%       3.61 ±  4%  perf-profile.children.cycles-pp.entry_SYSCALL_64_after_swapgs
>      12.79 ±  1%     -10.0%      11.50 ±  6%  perf-profile.children.cycles-pp.selinux_file_permission
>       1.70 ±  3%     -13.8%       1.46 ±  5%  perf-profile.self.cycles-pp.__fget_light
>       2.03 ±  2%     -11.6%       1.80 ±  6%  perf-profile.self.cycles-pp.entry_SYSCALL_64
>       4.11 ±  1%     -12.0%       3.61 ±  4%  perf-profile.self.cycles-pp.entry_SYSCALL_64_after_swapgs
>       5.85 ±  2%     -12.5%       5.12 ±  5%  perf-profile.self.cycles-pp.selinux_file_permission
>  1.472e+12 ±  0%      -5.5%  1.392e+12 ±  0%  perf-stat.branch-instructions
>       0.89 ±  0%      -6.0%       0.83 ±  0%  perf-stat.branch-miss-rate%
>  1.303e+10 ±  0%     -11.1%  1.158e+10 ±  0%  perf-stat.branch-misses
>  5.534e+08 ±  4%      -6.9%  5.151e+08 ±  1%  perf-stat.cache-references
>    9347877 ±  1%      +3.4%    9663609 ±  0%  perf-stat.context-switches
>  2.298e+12 ±  0%      -5.6%  2.168e+12 ±  0%  perf-stat.dTLB-loads
>  1.525e+12 ±  1%      -5.4%  1.442e+12 ±  0%  perf-stat.dTLB-stores
>  7.795e+12 ±  0%      -5.5%  7.363e+12 ±  0%  perf-stat.iTLB-loads
>  6.694e+12 ±  1%      -4.5%  6.391e+12 ±  2%  perf-stat.instructions
>       0.93 ±  0%      -5.5%       0.88 ±  0%  perf-stat.ipc
>     119024 ±  5%     -11.3%     105523 ±  8%  sched_debug.cfs_rq:/.exec_clock.max
>    5933459 ± 19%     +24.5%    7385120 ±  3%  sched_debug.cpu.nr_switches.max
>    1684848 ± 15%     +20.6%    2032107 ±  3%  sched_debug.cpu.nr_switches.stddev
>    5929704 ± 19%     +24.5%    7382036 ±  3%  sched_debug.cpu.sched_count.max
>    1684318 ± 15%     +20.6%    2031701 ±  3%  sched_debug.cpu.sched_count.stddev
>    2826278 ± 18%     +30.4%    3684493 ±  3%  sched_debug.cpu.sched_goidle.max
>     804195 ± 14%     +26.2%    1014783 ±  3%  sched_debug.cpu.sched_goidle.stddev
>    2969365 ± 19%     +24.3%    3692180 ±  3%  sched_debug.cpu.ttwu_count.max
>     843614 ± 15%     +20.5%    1016263 ±  3%  sched_debug.cpu.ttwu_count.stddev
>    2963657 ± 19%     +24.4%    3687897 ±  3%  sched_debug.cpu.ttwu_local.max
>     843104 ± 15%     +20.5%    1016333 ±  3%  sched_debug.cpu.ttwu_local.stddev
> 
> 
> 
>                            will-it-scale.time.user_time
> 
>   172 ++--------------------*--------*---*----------------------------------+
>   170 ++..*....*...*....*.      *..         .       ..*....  ..*...*....    |
>       *.                                     *....*.       *.           *...*
>   168 ++                                                                    |
>   166 ++                                                                    |
>       |                                                                     |
>   164 ++                                                                    |
>   162 ++                                                                    |
>   160 ++                                                                    |
>       |                              O            O                         |
>   158 ++                        O        O   O                              |
>   156 ++                    O                                               |
>       O            O                                                        |
>   154 ++       O        O                                                   |
>   152 ++--O-----------------------------------------------------------------+
> 
> 
>                           will-it-scale.time.system_time
> 
>   912 ++--------------------------------------------------------------------+
>   910 ++  O             O                                                   |
>       O        O   O                                                        |
>   908 ++                    O                                               |
>   906 ++                        O        O   O                              |
>   904 ++                             O            O                         |
>   902 ++                                                                    |
>       |                                                                     |
>   900 ++                                                                    |
>   898 ++                                                                    |
>   896 ++                                                                    |
>   894 ++                                                                  ..*
>       *...*....  ..*....                   ..*....*...*....*...*...*....*.  |
>   892 ++       *.       *...*...*....*...*.                                 |
>   890 ++--------------------------------------------------------------------+
> 
> 
>                              will-it-scale.per_thread_ops
> 
>   2.55e+06 ++---------------------------------------------------------------+
>    2.5e+06 ++ .*...*..    .*...*...           ..*.             .*..         |
>            |..        . ..         *...*....*.    ..   .*... ..    .        |
>   2.45e+06 *+          *                             ..     *       *...*...*
>    2.4e+06 ++                                       *                       |
>   2.35e+06 ++                                                               |
>    2.3e+06 ++                                                               |
>            |                                                                |
>   2.25e+06 ++                                                               |
>    2.2e+06 ++                      O                                        |
>   2.15e+06 ++  O                       O        O   O                       |
>    2.1e+06 ++          O       O                                            |
>            O       O                        O                               |
>   2.05e+06 ++              O                                                |
>      2e+06 ++---------------------------------------------------------------+
> 
> 	[*] bisect-good sample
> 	[O] bisect-bad  sample
> 
> 
> Disclaimer:
> Results have been estimated based on internal Intel analysis and are provided
> for informational purposes only. Any difference in system hardware or software
> design or configuration may affect actual performance.
> 
> 
> Thanks,
> Xiaolong

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