linux-kernel - Re: [PATCH v3 6/9] perf, x86: handle multiple records in PEBS buffer

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Date:	Mon, 28 Jul 2014 05:36:29 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	"Yan, Zheng" <zheng.z.yan@...el.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org, mingo@...nel.org, acme@...radead.org,
	eranian@...gle.com, andi@...stfloor.org
Subject: Re: [PATCH v3 6/9] perf, x86: handle multiple records in PEBS
 buffer

> I don't think this method works for interrupt threshold > 1 case. When collision
> happens, the hardware only create one PEBS record. The status in next record has
> nothing to do with the collision record.
>
Not even for the threshold == 1 case, because the same could happen with
a different PEBS event. Of course in any case it's very unlikely ...

 > 
> > So typically we'd have one event set and no problem, but in case there's
> > more we can reconstruct with such a backwards pass from a known good
> > state.
> > 
> > But when in doubt, we should drop the record, its the safest choice.
> 
> The problem is that, in some cases, each PEBS record has more than one events
> set, so we will drop all records.

Just dropping is fine imho, this should be rare.

-Andi
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