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From: Ingo Molnar <mingo@elte.hu>
To: Cyrill Gorcunov <gorcunov@gmail.com>
Cc: Don Zickus <dzickus@redhat.com>,
	Stephane Eranian <eranian@google.com>,
	Lin Ming <ming.m.lin@intel.com>,
	Peter Zijlstra <a.p.zijlstra@chello.nl>,
	Arnaldo Carvalho de Melo <acme@redhat.com>,
	Frederic Weisbecker <fweisbec@gmail.com>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH -tip, final] perf, x86: Add hw_watchdog_set_attr() in a sake of nmi-watchdog on P4
Date: Tue, 5 Jul 2011 15:10:05 +0200	[thread overview]
Message-ID: <20110705131005.GA5843@elte.hu> (raw)
In-Reply-To: <20110705121421.GU17941@sun>


* Cyrill Gorcunov <gorcunov@gmail.com> wrote:

> perf, x86: P4 PMU - Add hw_watchdog_set_attr helper to simulate cpu-cycles counting in nmi-watchdog
> 
> Because of constraints existed in Netburst PMU counting
> cpu cycles is allowed for one consumer only.
> 
> If the kernel is booted up with nmi-watchdog enabled
> the watchdog become a consumer of such event and there
> is no more room left for "perf top" and friends (ie any
> attempts to count cpu cycles simultaneously with nmi-watchdog
> doomed to fail).

Hm, what is the symptom - 'perf top' reports nothing?

If multiple users request cycles then perf will time-share them - 
this is what happens if you run many 'perf top' or 'perf stat' 
sessions in parallel for example. For example i just tried to run six 
separate 'perf top' in parallel - and all six worked fine.

So the question is, why does the NMI watchdog prevent 'perf top' from 
working on a P4?

Thanks,

	Ingo

  reply	other threads:[~2011-07-05 13:10 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-07-05 10:03 [PATCH -tip, final] perf, x86: Add hw_watchdog_set_attr() in a sake of nmi-watchdog on P4 Cyrill Gorcunov
2011-07-05 10:20 ` Ingo Molnar
2011-07-05 10:34   ` Cyrill Gorcunov
2011-07-05 10:59     ` Ingo Molnar
2011-07-05 11:05       ` Cyrill Gorcunov
2011-07-05 11:20         ` Ingo Molnar
2011-07-05 11:36           ` Cyrill Gorcunov
2011-07-05 11:44             ` Ingo Molnar
2011-07-05 11:49               ` Cyrill Gorcunov
2011-07-05 12:14                 ` Cyrill Gorcunov
2011-07-05 13:10                   ` Ingo Molnar [this message]
2011-07-05 13:17                     ` Peter Zijlstra
2011-07-05 13:31                       ` Ingo Molnar
2011-07-05 14:19                         ` Cyrill Gorcunov
2011-07-08 12:44                           ` Ingo Molnar
2011-07-05 14:20                         ` Peter Zijlstra
2011-07-05 14:40                         ` Peter Zijlstra
2011-07-05 14:56                           ` Ingo Molnar
2011-07-05 15:25                             ` Cyrill Gorcunov
2011-07-06  7:01                               ` Cyrill Gorcunov
2011-07-08 12:49                               ` Ingo Molnar
2011-07-08 13:01                                 ` Cyrill Gorcunov
2011-07-08 13:09                                   ` Ingo Molnar
2011-07-08 13:12                                   ` Cyrill Gorcunov
2011-07-05 13:26                     ` Cyrill Gorcunov
2011-07-05 12:24               ` Don Zickus
2011-07-05 12:26                 ` Cyrill Gorcunov
2011-07-05 12:44                   ` Don Zickus
2011-07-05 12:56                     ` Cyrill Gorcunov

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