linux-kernel - Re: [PATCH -v3] perf, x86: try to handle unknown nmis with running perfctrs

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Date:	Thu, 26 Aug 2010 17:14:24 -0400
From:	Don Zickus <dzickus@...hat.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Robert Richter <robert.richter@....com>,
	Cyrill Gorcunov <gorcunov@...il.com>,
	Lin Ming <ming.m.lin@...el.com>,
	"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 -v3] perf, x86: try to handle unknown nmis with running
 perfctrs

On Mon, Aug 23, 2010 at 10:53:39AM +0200, Ingo Molnar wrote:
> 
> * Ingo Molnar <mingo@...e.hu> wrote:
> 
> > 
> > * Don Zickus <dzickus@...hat.com> wrote:
> > 
> > > I'll test tip later today to see if I can reproduce it.
> > > 
> > > Cheers,
> > > Don
> > > 
> > > Ingo Molnar <mingo@...e.hu> wrote:
> > > 
> > > >
> > > >it's not working so well, i'm getting:
> > > >
> > > > Uhhuh. NMI received for unknown reason 00 on CPU 9.
> > > > Do you have a strange power saving mode enabled?
> > > > Dazed and confused, but trying to continue
> > > >
> > > >on a nehalem box, after a perf top and perf stat run.
> > 
> > FYI, it does not trigger on an AMD box.
> 
> Ok, to not hold up the perf/urgent flow i zapped these two commits for 
> the time being:
> 
>  4a31beb: perf, x86: Fix handle_irq return values
>  8e3e42b: perf, x86: Try to handle unknown nmis with an enabled PMU
> 
> We can apply them if they take a form that dont introduce a different 
> kind of (and more visible) regression.

So this patch fixes it, though I haven't convince myself why (perhaps
babysitting my 4 month old isn't helping :-))

The code now enters the loop and reprocesses the new status which properly
increments handled to 2 and thus the new logic takes care of it.

Cheers,
Don


diff --git a/arch/x86/kernel/cpu/perf_event_intel.c b/arch/x86/kernel/cpu/perf_event_intel.c
index 4539b4b..d16ebd8 100644
--- a/arch/x86/kernel/cpu/perf_event_intel.c
+++ b/arch/x86/kernel/cpu/perf_event_intel.c
@@ -738,6 +738,7 @@ again:
 
 	inc_irq_stat(apic_perf_irqs);
 	ack = status;
+	intel_pmu_ack_status(ack);
 
 	intel_pmu_lbr_read();
 
@@ -766,8 +767,6 @@ again:
 			x86_pmu_stop(event);
 	}
 
-	intel_pmu_ack_status(ack);
-
 	/*
 	 * Repeat if there is more work to be done:
 	 */
--
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