linux-kernel - Re: [PATCH v2] x86/mce: Distirbute the clear operation of mces_seen to Per-CPU rather than only monarch CPU

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Date:	Fri, 23 May 2014 14:50:41 -0700
From:	Tony Luck <tony.luck@...il.com>
To:	Chen Yucong <slaoub@...il.com>
Cc:	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>,
	"bp@...en8.de" <bp@...en8.de>,
	"ak@...ux.intel.com" <ak@...ux.intel.com>,
	"Huang, Ying" <ying.huang@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>
Subject: Re: [PATCH v2] x86/mce: Distirbute the clear operation of mces_seen
 to Per-CPU rather than only monarch CPU

On Thu, May 22, 2014 at 6:32 PM, Chen Yucong <slaoub@...il.com> wrote:
> As Naoya Horiguchi says, this patch also have a small benefit that it
> can reduce the processing time of monarch CPU.

This is indeed a benefit - but I'm not super worried about performance
of machine check handler.

>        /*
>         * Now clear the mces_seen of current CPU -*final - so that it
> does not
>         * reappear on the next mce.
>         */
>        memset(final, 0, sizeof(struct mce));
>        mce_wrmsrl(MSR_IA32_MCG_STATUS, 0);

But if the monarch hasn't managed to clean mces_seen, then
it certainly hasn't cleared MCG_STATUS ... so there can't be
a "next" mce that would see these old values. Any extra MCE
will result in system reset.

So we are not arguing that your patch is wrong - it just doesn't seem
to be any better that what we have now (except for an unimportant
small performance improvement).

-Tony
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