linux-kernel - Re: [RFC -tip] perf, x86: Add PERF_COUNT_HW_NMI

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Message-ID: <20110621164820.GC21641@sun>
Date:	Tue, 21 Jun 2011 20:48:20 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Stephane Eranian <eranian@...gle.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Don Zickus <dzickus@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	Lin Ming <ming.m.lin@...el.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Vince Weaver <vweaver1@...s.utk.edu>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [RFC -tip] perf, x86: Add PERF_COUNT_HW_NMI_WATCHDOG event v2

On Tue, Jun 21, 2011 at 06:20:56PM +0200, Stephane Eranian wrote:
> Cyrill,
> [repost because of MIME crap]

I saw first as well, sorry for delay, my isp is broken today :/

> 
> I admit I don't quite understand how this patch works around
> the limitation. In the end you are still going to program some cycle
> event into a P4 PMU register. So how it is going to free more counters
> for regular users?
> 
> 

  The key here is that we use that named non-sleeping ticks (as oprofile
did) for nmi-watchdog and it allows us to free "cpu-cycles" counter for
user needs. Of course we pick up one counter for this but it doesn't intersect
with "cpu-cycles" counter (because counters are grouped and can count only
specified events in each group). Stepane, should I post more details?

	Cyrill
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