linux-kernel - Re: [PATCH v3 17/17] x86/mce: Restore poll settings after storm subsides

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Message-ID: <20250513175543.GGaCOHn26isB18J9ig@fat_crate.local>
Date: Tue, 13 May 2025 19:55:43 +0200
From: Borislav Petkov <bp@...en8.de>
To: Yazen Ghannam <yazen.ghannam@....com>
Cc: x86@...nel.org, Tony Luck <tony.luck@...el.com>,
	linux-kernel@...r.kernel.org, linux-edac@...r.kernel.org,
	Smita.KoralahalliChannabasappa@....com,
	Qiuxu Zhuo <qiuxu.zhuo@...el.com>
Subject: Re: [PATCH v3 17/17] x86/mce: Restore poll settings after storm
 subsides

On Mon, May 12, 2025 at 11:43:15AM -0400, Yazen Ghannam wrote:
> The use case is "disable MCA polling". I just gave two examples of how
> this can be done.

Our documentation says:

                ignore_ce
                        disable features for corrected errors, e.g.
                        polling timer and CMCI.  All events reported as 
                        corrected are not cleared by OS and remained in its
                        error banks.

                        Usually this disablement is not recommended, however
                        if there is an agent checking/clearing corrected
                        errors (e.g. BIOS or hardware monitoring 
                        applications), conflicting with OS's error handling,
                        and you cannot deactivate the agent, then this option
                        will be a help.

it basically disables all: polling *and* CMCI.

So why do we even bother with storms?

> We can focus on "check_interval=0". The user wants to disable MCA
> polling and rely only on interrupts. They still want to see the CEs.

Is that a use case we support?

Where is that documented?

I can see why someone would want to avoid the recurrent polling but I'm not
sure we explicitly say that somewhere in the text...

> When the storm ends, the kernel should go back to how things were before
> the storm. If there was a timer before, then go back to the old
> interval. If there was *not* a timer before, then delete/remove the
> timer.

That I agree with.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette