linux-kernel - Re: [PATCH] x86/mce: Distirbute the clear operation of mces_seen to Per-CPU rather than only monarch CPU

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Date:	Mon, 19 May 2014 09:55:40 +0800
From:	Chen Yucong <slaoub@...il.com>
To:	Borislav Petkov <bp@...en8.de>
Cc:	tony.luck@...el.com, linux-kernel@...r.kernel.org,
	linux-edac@...r.kernel.org
Subject: Re: [PATCH] x86/mce: Distirbute the clear operation of mces_seen to
 Per-CPU rather than only monarch CPU

On Sun, 2014-05-18 at 18:35 +0200, Borislav Petkov wrote:
> On Sun, May 18, 2014 at 11:05:04PM +0800, Chen Yucong wrote:a
> > mces_seen is a Per-CPU variable which should only be accessed by
> > Per-CPU as possible. So the clear operation of mces_seen should also
> > be lcoal to Per-CPU rather than monarch CPU.
> 
> No, you need to do the cleaning in mce_reign because the monarch cpu has
> to run last after all other cpus have scanned their mce banks.
> 
But all other CPUs also have to wait monarch CPU to exit from mce_end. 
What's the difference between monarch CPU and Per-CPU for clearing
mces_seen? In practice, there is no difference between them. If we use
monarch CPU to clear mces_seen, then Per-CPU variable can not play out
its advantage.

> > Meanwhile, there is also a potential risk that mces_seen will not
> > be be cleared if a timeout occors in mce_end for monarch CPU. As a
> > reuslt, the stale value of mces_seen will reappear on the next mce.
> 
> If that happens, we have a bigger problem.
Well, in that case, why is there a need for time-out machine in MCE
handler?

Any potential risks --both logical and realistic-- should be avoided as
possible if there are no more questions and performance penalty.

thx!
cyc 
> 
> Is that a real issue you're trying to address?



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