linux-kernel - Re: [PATCH] perf, x86: catch spurious interrupts after disabling counters

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Date:	Thu, 30 Sep 2010 14:33:38 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Stephane Eranian <eranian@...gle.com>
Cc:	Robert Richter <robert.richter@....com>,
	Don Zickus <dzickus@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	"gorcunov@...il.com" <gorcunov@...il.com>,
	"fweisbec@...il.com" <fweisbec@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"ying.huang@...el.com" <ying.huang@...el.com>,
	"ming.m.lin@...el.com" <ming.m.lin@...el.com>,
	"yinghai@...nel.org" <yinghai@...nel.org>,
	"andi@...stfloor.org" <andi@...stfloor.org>
Subject: Re: [PATCH] perf, x86: catch spurious interrupts after disabling
 counters

On Fri, 2010-09-24 at 15:38 +0200, Stephane Eranian wrote:
> > I don't like the approach of disabling all counters in the nmi
> > handler. First, it stops counting and thus may falsify
> > measurement. Second, it introduces much overhead doing a rd-/wrmsrl()
> > for each counter.
> >
> But that's exactly what is going on the Intel side. PMU is stopped on interrupt.
> An argument for this is that you don't necessarily want to monitor across
> the PMU handler, i.e., the overhead you introduce.

Right, its really a question of what you want to measure. I prefer not
to measure the measuring itself, things are hard enough to interpret
already.

Then again, the Intel stuff has a real handy way to disable the whole
PMU, unlike the AMD bits where you need to iterate each counter
individually.
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