linux-kernel - Re: [V3][PATCH 0/6] x86, nmi: new NMI handling routines

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Message-ID: <20110826143949.GX2067@redhat.com>
Date:	Fri, 26 Aug 2011 10:39:49 -0400
From:	Don Zickus <dzickus@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	x86@...nel.org, Andi Kleen <andi@...stfloor.org>,
	Robert Richter <robert.richter@....com>, ying.huang@...el.com,
	LKML <linux-kernel@...r.kernel.org>, paulmck@...ux.vnet.ibm.com
Subject: Re: [V3][PATCH 0/6] x86, nmi: new NMI handling routines

On Fri, Aug 26, 2011 at 11:44:57AM +0200, Peter Zijlstra wrote:
> On Thu, 2011-08-25 at 12:45 -0400, Don Zickus wrote:
> > I spent some time hacking and came up with this patch.  I tested it on my
> > core2quad machine trying to enable all the NMI handler I could, mainly
> > perf and kgdb (and oprofile too when perf was disabled).  Everything seems
> > to work correctly.  If people are ok with this approach, I'll try and test
> > this on more machines. 
> 
> Right, code looks OK, the only worry that remains is overhead, always
> running all handlers must cost..

Yeah nothing is free.  My only counter argument is I removed the case
statements in the handlers, so it speeds things up a tiny bit.  Also most
machines only seem to have perf and the arch_backtrace handler registered,
with modern intel boxes probably registering the ghes handler too.

There really isn't much there, at least currently.  I would break up the
handler more if I knew a quicker way to distinguish between something like
a self-IPI NMI vs. an on-chip NMI like perf.  Then again those NMIs
probably aren't latched differently unlike the external one sitting in the
IOAPIC(??).

Cheers,
Don
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