linux-kernel - RE: [PATCH v9 2/3] x86/mce: Add per-bank CMCI storm mitigation

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Date:   Wed, 11 Oct 2023 17:23:54 +0000
From:   "Luck, Tony" <tony.luck@...el.com>
To:     "Tang, Feng" <feng.tang@...el.com>
CC:     "Sang, Oliver" <oliver.sang@...el.com>,
        "oe-lkp@...ts.linux.dev" <oe-lkp@...ts.linux.dev>,
        lkp <lkp@...el.com>,
        "linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>,
        "Huang, Ying" <ying.huang@...el.com>,
        "Yin, Fengwei" <fengwei.yin@...el.com>,
        Borislav Petkov <bp@...en8.de>,
        "Yazen Ghannam" <yazen.ghannam@....com>,
        "Smita.KoralahalliChannabasappa@....com" 
        <Smita.KoralahalliChannabasappa@....com>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "patches@...ts.linux.dev" <patches@...ts.linux.dev>
Subject: RE: [PATCH v9 2/3] x86/mce: Add per-bank CMCI storm mitigation

> 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.

If adding (removing, changing) per-cpu variables can cause 8% performance
changes, then maybe there needs to be some way to insulate the builds
from these side effects (as was done with the 64-byte function alignment).
I've no ideas on how to achieve that :-(

"storm_desc" is a largish per-cpu variable at 1568 bytes. But that doesn't
quite get it into the top 20.

In the config used for my kernel build, it does appear just before a bunch
of interrupt related per-cpu variables. Those might be sensitive to alignment?

000000000001ff40 d smca_misc_banks_map
000000000001ff48 d bank_map
000000000001ff50 d threshold_banks
000000000001ff60 d storm_desc
0000000000020580 d tsc_adjust
00000000000205c0 d lapic_events
00000000000206c0 d vector_cleanup
0000000000020720 D __uv_cpu_info
0000000000020738 d ipi_mask

-Tony