linux-kernel - Re: [x86/modules] f2c65fb322: will-it-scale.per_process

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Date:   Thu, 18 Jul 2019 17:59:08 +0000
From:   Nadav Amit <namit@...are.com>
To:     kernel test robot <rong.a.chen@...el.com>
CC:     Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...capital.net>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...el.com>,
        "H. Peter Anvin" <hpa@...or.com>, Jessica Yu <jeyu@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Rik van Riel <riel@...riel.com>,
        LKML <linux-kernel@...r.kernel.org>, "lkp@...org" <lkp@...org>
Subject: Re: [x86/modules]  f2c65fb322:  will-it-scale.per_process_ops -2.9%
 regression

> On Jul 18, 2019, at 2:50 AM, kernel test robot <rong.a.chen@...el.com> wrote:
> 
> Greeting,
> 
> FYI, we noticed a -2.9% regression of will-it-scale.per_process_ops due to commit:
> 
> 
> commit: f2c65fb3221adc6b73b0549fc7ba892022db9797 ("x86/modules: Avoid breaking W^X while loading modules")
> https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Fkernel.googlesource.com%2Fpub%2Fscm%2Flinux%2Fkernel%2Fgit%2Ftorvalds%2Flinux.git&amp;data=02%7C01%7Cnamit%40vmware.com%7Cdfe19d72eecd46a93fc508d70b65652b%7Cb39138ca3cee4b4aa4d6cd83d9dd62f0%7C0%7C0%7C636990402460329367&amp;sdata=9MHPlha0MIkDWKe%2BurDDr0QRDMtJ3pPACgDtVXy8pL4%3D&amp;reserved=0 master
> 
> in testcase: will-it-scale
> on test machine: 192 threads Intel(R) Xeon(R) CPU @ 2.20GHz with 192G memory
> with following parameters:
> 
> 	nr_task: 100%
> 	mode: process
> 	test: poll1
> 	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://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fantonblanchard%2Fwill-it-scale&amp;data=02%7C01%7Cnamit%40vmware.com%7Cdfe19d72eecd46a93fc508d70b65652b%7Cb39138ca3cee4b4aa4d6cd83d9dd62f0%7C0%7C0%7C636990402460329367&amp;sdata=YmsJebf0t3yyo7KMCdUu6VIOysebmB%2Fc7huxkOe5cV0%3D&amp;reserved=0

I don’t understand how this patch has any impact on this workload.

I ran it and set a function tracer for any function that is impacted by this
patch:

  # cd /sys/kernel/debug/tracing
  # echo text_poke_early > set_ftrace_filter
  # echo module_alloc >> set_ftrace_filter
  # echo bpf_int_jit_compile >> set_ftrace_filter
  # tail -f trace

Nothing came up. Can you please check if you see any of them invoked on your
setup? Perhaps you have some bpf filters being installed, although even then
this is a one-time (small) overhead for each process invocation.