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Date:   Wed, 11 Oct 2023 23:42:26 +0800
From:   Feng Tang <feng.tang@intel.com>
To:     "Luck, Tony" <tony.luck@intel.com>
CC:     "Sang, Oliver" <oliver.sang@intel.com>,
        "oe-lkp@lists.linux.dev" <oe-lkp@lists.linux.dev>,
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        "Huang, Ying" <ying.huang@intel.com>,
        "Yin, Fengwei" <fengwei.yin@intel.com>,
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Subject: Re: [PATCH v9 2/3] x86/mce: Add per-bank CMCI storm mitigation
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On Wed, Oct 11, 2023 at 11:16:46PM +0800, Luck, Tony wrote:
> > kernel test robot noticed a -8.8% regression of stress-ng.clock.ops_per_sec on:
> >
> >
> > commit: 26bff7b04b829cccc6a97726d6398391a62e34ef ("[PATCH v9 2/3] x86/mce: Add per-bank CMCI storm mitigation")
> > url: https://github.com/intel-lab-lkp/linux/commits/Tony-Luck/x86-mce-Remove-old-CMCI-storm-mitigation-code/20231005-024047
> > patch link: https://lore.kernel.org/all/20231004183623.17067-3-tony.luck@intel.com/
> > patch subject: [PATCH v9 2/3] x86/mce: Add per-bank CMCI storm mitigation
> >
> > testcase: stress-ng
> > test machine: 64 threads 2 sockets Intel(R) Xeon(R) Gold 6346 CPU @ 3.10GHz (Ice Lake) with 256G memory
> > parameters:
> >
> >       nr_threads: 10%
> >       disk: 1HDD
> >       testtime: 60s
> >       fs: ext4
> >       class: os
> >       test: clock
> >       cpufreq_governor: performance
> >
> >
> >
> >
> > If you fix the issue in a separate patch/commit (i.e. not just a new version of
> > the same patch/commit), kindly add following tags
> > | Reported-by: kernel test robot <oliver.sang@intel.com>
> > | Closes: https://lore.kernel.org/oe-lkp/202310111637.dee70328-oliver.sang@intel.com
> 
> Is the test injecting massive numbers of corrected memory errors? The code in this patch
> is only executed when handling CMCI interrupts, or polling machine check banks (at most
> once per second).
> 
> I'm guessing this report is just because alignment of some hot path code changed.

IIRC, CONFIG_DEBUG_FORCE_FUNCTION_ALIGN_64B was enabled in 0Day's
kernel config for quite a while, to force each funtion's start
address aligned on 64 bytes. Don't know if this has been changed
recently.

Also I noticed the patch introduce a new per-cpu variable 'storm_desc",
if the function address is 64B aligned, then per-cpu data alignment
may be related.

Thanks,
Feng

> 
> -Tony