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

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Message-ID: <20100804161046.GC5130@lenovo>
Date:	Wed, 4 Aug 2010 20:10:46 +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 11:50:02AM -0400, Don Zickus wrote:
...
> > 
> > Well, first I guess having Yinghai CC'ed is a bonus ;)
> > The second thing is that I don't get why perf handler can't be _last_
> > call in default_do_nmi, if there were any nmi with reason (serr or parity)
> > I think they should be calling first which of course don't eliminate
> > the former issue but somewhat make it weaken.
> 
> 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).

> Unknown nmis are unknown nmis, nobody is claiming them.  Even worse, there
> are customers that want to register their nmi handler below the perf
> handler to claim all the unknown nmis, so they can be logged on the system
> before being rebooted.

well, perhaps we might need some kind of perf_chain in notifier code and
call for it after die_nmi chain, so the customers you mention may add own
chain for being called last.

> 
> Cheers,
> Don
> 
	-- Cyrill
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