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Date: Fri, 27 Aug 2010 09:51:32 +0200
From: Robert Richter <robert.richter@amd.com>
To: Don Zickus <dzickus@redhat.com>
CC: Ingo Molnar <mingo@elte.hu>, Peter Zijlstra <peterz@infradead.org>,
        Cyrill Gorcunov <gorcunov@gmail.com>, Lin Ming <ming.m.lin@intel.com>,
        "fweisbec@gmail.com" <fweisbec@gmail.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "Huang, Ying" <ying.huang@intel.com>, Yinghai Lu <yinghai@kernel.org>,
        Andi Kleen <andi@firstfloor.org>
Subject: Re: [PATCH -v3] perf, x86: try to handle unknown nmis with running
 perfctrs
Message-ID: <20100827075132.GD22783@erda.amd.com>
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 <20100820152510.GA4167@elte.hu>
 <20100823085339.GA26713@elte.hu>
 <20100826211424.GQ4879@redhat.com>
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On 26.08.10 17:14:24, Don Zickus wrote:
> 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);

Yes, not immediately ack'ing the status was suspect to me too. Though
it must then be the same counter that retriggers. Or, it is a cpu
bug. You could add a debug print of the status register for the case
the loop is reentered, would be interesting...

Thank for fixing this.

-Robert

>  
>  	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:
>  	 */
> 

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