linux-kernel - Re: [PATCH 1/6] x86-mce: Modify CMCI poll interval to adjust for small check

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Message-ID: <20140709191747.GB5249@pd.tnic>
Date:	Wed, 9 Jul 2014 21:17:47 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Havard Skinnemoen <hskinnemoen@...gle.com>
Cc:	Tony Luck <tony.luck@...el.com>, linux-kernel@...r.kernel.org,
	Ewout van Bekkum <ewout@...gle.com>
Subject: Re: [PATCH 1/6] x86-mce: Modify CMCI poll interval to adjust for
 small check_interval values.

On Wed, Jul 09, 2014 at 10:09:21AM -0700, Havard Skinnemoen wrote:
> From: Ewout van Bekkum <ewout@...gle.com>
> 
> The CMCI poll interval was updated to pick the minimum interval between
> the original 30 seconds and the check_interval divided by 8 (minimum of
> 3 polls).

Why min 3 polls? How do you come up with exactly that frequency?

> This resolves a bug where the CMCI storm handler is unable to return to
> interrupt mode from polling mode, if the check_interval shorter than the
> CMCI poll interval. This problem is caused by the mce_timer_fn function
> which only allows the poll interval to be incremented up to the
> check_interval, while the mce_intel_adjust_timer function requires the
> poll interval to be greater than the CMCI poll interval before leaving
> the CMCI_STORM_ACTIVE state.

Interesting. So it seems you guys want to set the check_interval to
something < 30 secs.

Out of curiosity, what is your use case which requires such small
check_interval setting?

Maybe we need to redesign and simplify this intervals thing to make it
more user-friendly...

Btw, on a related note, we're working on a small mechanism which
collects correctable errors in the kernel and when a certain count for a
physical error address has been reached, we soft-offline that page. We'd
appreciate it if you guys took a look and told us whether it makes sense
to you:

http://lkml.kernel.org/r/1404242623-10094-1-git-send-email-bp@alien8.de

Thanks.

-- 
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.
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