linux-kernel - Re: [V6][PATCH 4/6] x86, nmi: add in logic to handle multiple events and unknown NMIs

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Message-ID: <20111003131328.GW5795@redhat.com>
Date:	Mon, 3 Oct 2011 09:13:28 -0400
From:	Don Zickus <dzickus@...hat.com>
To:	Avi Kivity <avi@...hat.com>
Cc:	Robert Richter <robert.richter@....com>,
	"x86@...nel.org" <x86@...nel.org>,
	Andi Kleen <andi@...stfloor.org>,
	Peter Zijlstra <peterz@...radead.org>,
	"ying.huang@...el.com" <ying.huang@...el.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"paulmck@...ux.vnet.ibm.com" <paulmck@...ux.vnet.ibm.com>,
	"jeremy@...p.org" <jeremy@...p.org>
Subject: Re: [V6][PATCH 4/6] x86, nmi:  add in logic to handle multiple
 events and unknown NMIs

On Sun, Oct 02, 2011 at 12:07:16PM +0200, Avi Kivity wrote:
> >Right.  Avi, Jeremy what was your objection that needed this optimization
> >in the first place?
> >
> 
> First, iterating over all NMI sources is going to be slow, and a lot
> more so in a guest.  This reduces the performance of perf.

I understand and agree.  The only positive I can offer is most machines
will most likely only have two NMI handlers registered: perf and
arch_backtrace.  So any slowness should be minimal.  We might even be able
to code up arch_backtrace to register its NMI handler when it is called to 
minimize the the number of NMI sources even more.

Cheers,
Don

> 
> Second, I wanted to use NMIs as a way of waking up a vcpu sleeping
> with interrupts disabled (in the context of Jeremy's paravirt
> spinlock patches).  Looks like we'll have to use paravirtualization
> for that.


> 
> -- 
> error compiling committee.c: too many arguments to function
> 
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