linux-kernel - Re: A question of perf NMI handler

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Date:	Wed, 4 Aug 2010 20:39:30 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Don Zickus <dzickus@...hat.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Robert Richter <robert.richter@....com>,
	Lin Ming <ming.m.lin@...el.com>, Ingo Molnar <mingo@...e.hu>,
	"fweisbec@...il.com" <fweisbec@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Huang, Ying" <ying.huang@...el.com>,
	Yinghai Lu <yinghai@...nel.org>
Subject: Re: A question of perf NMI handler

On Wed, Aug 04, 2010 at 12:20:26PM -0400, Don Zickus wrote:
...
> > > 
> > > Because the reason registers are never set.  If they were, then the code
> > > wouldn't have to walk the notify_chain. :-)
> > > 
> > 
> > maybe we're talking about different things. i meant that if there is nmi
> > with a reason (from 0x61) the handling of such nmi should be done before
> > notify_die I think (if only I not miss something behind).
> 
> No we are talking about the same thing. :-)  And that code is already

seems not actually ;)

> there.  The problem is the bits in register 0x61 are not always set
> correctly in the case of SERRs (well at least in all the cases I have
> dealt with).  So you can easily can a flood of unknown nmis from an SERR
> and register 0x61 would have the PERR/SERR bits set to 0.  Fun, huh?

if there is nothing in nmi_sc the code flows into another branch. And
it hits the problem of perf events eating all nmi giving no chance the
others. So we take if (!(reason & 0xc0)) case and hit DIE_NMI_IPI
(/me scratching the head why it's not under CONFIG_X86_LOCAL_APIC) and
drop all code, unpleasant.

> 
> Cheers,
> Don
> 
	-- Cyrill
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