linux-kernel - Re: [tip:perf/urgent] perf, x86: Catch spurious interrupts after disabling counters

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Message-ID: <AANLkTikvYreYiyCbGeG02j+r4dWVLRH7BqeeG9O=VTNN@mail.gmail.com>
Date:	Wed, 29 Sep 2010 17:33:07 +0200
From:	Stephane Eranian <eranian@...gle.com>
To:	Cyrill Gorcunov <gorcunov@...il.com>
Cc:	Robert Richter <robert.richter@....com>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"hpa@...or.com" <hpa@...or.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"yinghai@...nel.org" <yinghai@...nel.org>,
	"andi@...stfloor.org" <andi@...stfloor.org>,
	"peterz@...radead.org" <peterz@...radead.org>,
	"ying.huang@...el.com" <ying.huang@...el.com>,
	"fweisbec@...il.com" <fweisbec@...il.com>,
	"ming.m.lin@...el.com" <ming.m.lin@...el.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"dzickus@...hat.com" <dzickus@...hat.com>,
	"mingo@...e.hu" <mingo@...e.hu>
Subject: Re: [tip:perf/urgent] perf, x86: Catch spurious interrupts after
 disabling counters

Robert,

There is something else bothering me with cpuc->running.

It is not reset outside of the interrupt handler. So what if
event scheduling shuffles things around and an event is
moved somewhere else. Don't you need to clear the
cpuc->running[idx] for the old counter index?


On Wed, Sep 29, 2010 at 5:27 PM, Cyrill Gorcunov <gorcunov@...il.com> wrote:
> On Wed, Sep 29, 2010 at 05:12:53PM +0200, Robert Richter wrote:
>> On 29.09.10 17:01:40, Robert Richter wrote:
>> > Right, I wasn't remembering correctly, it was P6 and core. And yes, P4
>> > requires the fix. Will send a patch for this.
>>
>> Ok, Cyrill is sending the patch.
>>
>> Thanks,
>>
>> -Robert
>>
>
> Managed to implement it earlier then I thought.
>
>  Cyrill
> ---
> Subject: [PATCH -tip] perf, x86: Handle in flight IRQs on P4 platform
>
> Stephane reported we've missed to guard P4 platform
> against spurious in-flight performance IRQs. Fix it.
>
> [ the patch is a complement to commit 63e6be6d98e1 ]
>
> Reported-by: Stephane Eranian <eranian@...gle.com>
> Signed-off-by: Cyrill Gorcunov <gorcunov@...nvz.org>
> CC: Robert Richter <robert.richter@....com>
> CC: Lin Ming <ming.m.lin@...el.com>
> ---
>  arch/x86/kernel/cpu/perf_event_p4.c |    6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
>
> Index: linux-2.6.git/arch/x86/kernel/cpu/perf_event_p4.c
> =====================================================================
> --- linux-2.6.git.orig/arch/x86/kernel/cpu/perf_event_p4.c
> +++ linux-2.6.git/arch/x86/kernel/cpu/perf_event_p4.c
> @@ -904,8 +904,12 @@ static int p4_pmu_handle_irq(struct pt_r
>        for (idx = 0; idx < x86_pmu.num_counters; idx++) {
>                int overflow;
>
> -               if (!test_bit(idx, cpuc->active_mask))
> +               if (!test_bit(idx, cpuc->active_mask)) {
> +                       /* catch in-flight IRQs */
> +                       if (__test_and_clear_bit(idx, cpuc->running))
> +                               handled++;
>                        continue;
> +               }
>
>                event = cpuc->events[idx];
>                hwc = &event->hw;
>
--
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