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

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Date:	Thu, 21 Oct 2010 10:53:57 +0800
From:	Huang Ying <ying.huang@...el.com>
To:	Don Zickus <dzickus@...hat.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, 2010-10-21 at 10:37 +0800, Don Zickus wrote:
> On Thu, Oct 21, 2010 at 09:25:09AM +0800, Huang Ying wrote:
> > On Thu, 2010-10-21 at 09:18 +0800, Don Zickus wrote:
> > > 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.
> > 
> > If we can guarantee that these NMIs will be only sent to one CPU, I am
> > fine with trylock.
> 
> I guess I assumed the BIOS would only use the bsp CPU for the NMI, which
> would be passed on to the kernel.  Otherwise what happens if an NMI
> happens while the kernel is still bringing up the first cpu and it is
> routed to another CPU or if we boot with MAX_CPUS=1?

After CPU hot-remove (should go through BIOS), BIOS may route the NMI to
other CPU I think. That should have no above issues. The question here
is that, BIOS will route different NMIs to one CPU or several CPUs?

Best Regards,
Huang Ying


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