linux-kernel - Re: [PATCH] perf, x86: Add workaround for MEM_*

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Message-ID: <20130501191342.GH17814@two.firstfloor.org>
Date:	Wed, 1 May 2013 21:13:42 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Stephane Eranian <eranian@...gle.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Andi Kleen <andi@...stfloor.org>,
	"mingo@...e.hu" <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] perf, x86: Add workaround for MEM_*_RETIRED errata BV98

> Unfortunately, Andi's patch fails to correct the problem though
> it is the right approach. As he said, the problem is unfortunately

perf stat -a / record -a / top will work.

The case it doesn't fix is per thread when the other sibling
is not running a counter.

Essentially with the patch you may still get under-counting
on these specific events if they run per thread (or are really
unlucky in multiplexing), but never over-counting on anything.

In the past Ingo's guidance was to focus on the most common 
use cases, which I think this patch does.

It would be possible to fix the per thread mode too, but it would
need quite a bit of new infrastructure and I have doubts that's 
worth it.

-Andi
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