linux-kernel - Re: [PATCH 14/34] perf, x86: Avoid checkpointed counters causing excessive TSX aborts

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Message-ID: <1350997423.13456.21.camel@twins>
Date:	Tue, 23 Oct 2012 15:03:43 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	x86@...nel.org, linux-kernel@...r.kernel.org, acme@...hat.com,
	eranian@...gle.com, Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH 14/34] perf, x86: Avoid checkpointed counters causing
 excessive TSX aborts

On Thu, 2012-10-18 at 16:19 -0700, Andi Kleen wrote:
> @@ -1079,6 +1079,17 @@ static void intel_pmu_enable_event(struct perf_event *event)
>  int intel_pmu_save_and_restart(struct perf_event *event)
>  {
>         x86_perf_event_update(event);
> +       /*
> +        * For a checkpointed counter always reset back to 0.  This
> +        * avoids a situation where the counter overflows, aborts the
> +        * transaction and is then set back to shortly before the
> +        * overflow, and overflows and aborts again.
> +        */
> +       if (event->hw.config & HSW_INTX_CHECKPOINTED) {

Would an unlikely() make sense there? Most events won't have this set.

> +               /* No race with NMIs because the counter should not be armed */
> +               wrmsrl(event->hw.event_base, 0);
> +               local64_set(&event->hw.prev_count, 0);
> +       }
>         return x86_perf_event_set_period(event);
>  } 
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