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

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Message-ID: <20100810172451.GD6893@lenovo>
Date:	Tue, 10 Aug 2010 21:24:51 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Robert Richter <robert.richter@....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 Tue, Aug 10, 2010 at 06:41:24PM +0200, Robert Richter wrote:
> 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.
> 

It gets masked on NMI arrival, at least for some models (Core Duo, P4,
P6 M and I suspect more theh that, that was the reason oprofile has
it, also there is a note in SDM V3a page 643).

> -Robert
> 
> -- 
> Advanced Micro Devices, Inc.
> Operating System Research Center
> 
	-- Cyrill
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