linux-kernel - Re: [PATCH -tip, final] perf, x86: Add hw_watchdog_set

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Date:	Tue, 5 Jul 2011 08:24:05 -0400
From:	Don Zickus <dzickus@...hat.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Cyrill Gorcunov <gorcunov@...il.com>,
	Stephane Eranian <eranian@...gle.com>,
	Lin Ming <ming.m.lin@...el.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -tip, final] perf, x86: Add hw_watchdog_set_attr() in a
 sake of nmi-watchdog on P4

On Tue, Jul 05, 2011 at 01:44:37PM +0200, Ingo Molnar wrote:
> > Probably I miss something and you mean something completely different?
> 
> What i am missing is that you have not pointed out the *core problem* 
> you are fixing and it's not obvious from the changelog either!

Cyril,

I think you didn't explain the fact that without this patch if you enable
nmi_watchdog, then the 'perf' tool doesn't work on a P4.  This is bad for
end users.  It seems like with all the P4 register coupling an end user
can run either the nmi_watchdog _or_ perf but not both.

For RHEL-6 this was bad because we like to enable the nmi_watchdog.

This patch does some magic and allows the end user to use the nmi_watchdog
_and_ perf concurrently (a common expected behaviour).

I hope that clears things up Ingo.

Cheers,
Don
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