linux-kernel - Re: [PATCH 4/5] x86, NMI: Allow NMI reason io port (0x61) to be processed on any CPU

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Message-ID: <20101021011813.GH19090@redhat.com>
Date:	Wed, 20 Oct 2010 21:18:13 -0400
From:	Don Zickus <dzickus@...hat.com>
To:	Huang Ying <ying.huang@...el.com>
Cc:	Robert Richter <robert.richter@....com>,
	"mingo@...e.hu" <mingo@...e.hu>,
	"andi@...stfloor.org" <andi@...stfloor.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"peterz@...radead.org" <peterz@...radead.org>
Subject: Re: [PATCH 4/5] x86, NMI: Allow NMI reason io port (0x61) to be
 processed on any CPU

On Thu, Oct 21, 2010 at 08:40:07AM +0800, Huang Ying wrote:
> On Wed, 2010-10-20 at 22:27 +0800, Don Zickus wrote:
> > I thought the point of this patch was to remove that restriction in the
> > nmi handler, which would allow future patches to re-route these NMIs to
> > another cpu, thus finally allowing people to hot-remove the bsp cpu, no?
> 
> Yes. We just want to make it possible to hot-remove the bsp cpu. Because
> IOAPIC is configurable, I think it is possible to configure IOAPIC to
> send PCI SERR NMI to one CPU while IOCK NMI to another CPU. Why not
> support this situation too? It does not harm anything but performance to

Why would we want to?  It seems simpler to have one cpu dedicated to
handling the external NMIs.

> use raw_spin_lock() instead of raw_spin_trylock() here. And for hardware
> error processing, performance is not so important in fact.

I don't know.  I was always a little uncomfortable with a spin_lock there,
so I am more supportive of a trylock.

Cheers,
Don
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