linux-kernel - RE: [PATCH] x86: auto poll/interrupt mode switch for CMC to stop CMC storm

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Date:	Wed, 23 May 2012 17:01:54 +0000
From:	"Luck, Tony" <tony.luck@...el.com>
To:	Thomas Gleixner <tglx@...utronix.de>,
	Chen Gong <gong.chen@...ux.intel.com>
CC:	"bp@...64.org" <bp@...64.org>, "x86@...nel.org" <x86@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>
Subject: RE: [PATCH] x86: auto poll/interrupt mode switch for CMC to stop
 CMC storm

> What's the point of doing this work? Why can't we just do that on the
> CPU which got hit by the MCE storm and leave the others alone? They
> either detect it themself or are just not affected. 

CMCI gets broadcast to all threads on a socket. So
if one cpu has a problem, many cpus have a problem :-(
Some machine check banks are local to a thread/core,
so we need to make sure that the CMCI gets taken by
someone who can actually see the bank with the problem.
The others are collateral damage - but this means there
is even more reason to do something about a CMCI storm
as the effects are not localized.

> What's wrong with doing that strictly per cpu and avoid the whole
> global state horror?

Is that less of a horror? We'd have some cpus polling and some
taking CMCI (in somewhat arbitrary and ever changing combinations).
I'm not sure which is less bad.

-Tony
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