linux-kernel - Re: [PATCH] perf, x86: try to handle unknown nmis with running perfctrs

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Date:	Tue, 10 Aug 2010 18:41:24 +0200
From:	Robert Richter <robert.richter@....com>
To:	Cyrill Gorcunov <gorcunov@...il.com>
CC:	Don Zickus <dzickus@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	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>,
	Andi Kleen <andi@...stfloor.org>
Subject: Re: [PATCH] perf, x86: try to handle unknown nmis with running
 perfctrs

On 10.08.10 12:16:27, Cyrill Gorcunov wrote:
> On Tue, Aug 10, 2010 at 09:42:00AM +0200, Robert Richter wrote:
> > On 09.08.10 16:02:45, Cyrill Gorcunov wrote:
> > 
> > > > @@ -1222,14 +1245,12 @@ perf_event_nmi_handler(struct notifier_block *self,
> > > >  	regs = args->regs;
> > > >  
> > > >  	apic_write(APIC_LVTPC, APIC_DM_NMI);
> > > 
> > > If only I'm not missing something this apic_write should go up to
> > > "case DIE_NMIUNKNOWN" site, no?
> > 
> > This seems to be code from the non-nmi implementation and can be
> > removed at all, which should be a separate patch. The vector is
> > already set up.
> > 
> > -Robert
> >
> 
> No, this is just a short way to unmask LVTPC (which is required for
> cpus). Actually lookig into this snippet I found that in p4 pmu
> I've made one redundant unmaksing operation. will update as only
> this area settle down.

The vector is setup in hw_perf_enable() and then never masked. The
perfctrs nmi is alwayes enabled since then. I still see no reason for
unmasking it again with every nmi. Once you handle the nmi it is also
enabled.

-Robert

-- 
Advanced Micro Devices, Inc.
Operating System Research Center

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