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Date: Tue, 21 Jun 2011 21:02:29 +0400
From: Cyrill Gorcunov <gorcunov@gmail.com>
To: Stephane Eranian <eranian@google.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>, Don Zickus <dzickus@redhat.com>,
        Ingo Molnar <mingo@elte.hu>, Lin Ming <ming.m.lin@intel.com>,
        Arnaldo Carvalho de Melo <acme@redhat.com>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Vince Weaver <vweaver1@eecs.utk.edu>,
        lkml <linux-kernel@vger.kernel.org>
Subject: Re: [RFC -tip] perf, x86: Add PERF_COUNT_HW_NMI_WATCHDOG event v2
Message-ID: <20110621170229.GD21641@sun>
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On Tue, Jun 21, 2011 at 08:48:20PM +0400, Cyrill Gorcunov wrote:
...
> 
>   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

  Stephane, I think I have a shorter explanation -- the counter is still borrowed
(there is no magic ;) but this counter is less loaded than anything else (in
terms of restrictions) so since CPU cycles is a way more popular now it's allowed
to count them simultaneously with nmi-watchdog, but again  -- this means
another set of events can't work and if (for some reason) user needs this counter
he has to disable nmi-watchdog.

	Cyrill
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