linux-kernel - Re: introduce NMI_AUTO as nmi

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Message-ID: <20100113162534.GX24885@redhat.com>
Date:	Wed, 13 Jan 2010 11:25:34 -0500
From:	Don Zickus <dzickus@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ingo Molnar <mingo@...e.hu>, Cyrill Gorcunov <gorcunov@...il.com>,
	aris@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: introduce NMI_AUTO as nmi_watchdog option

On Wed, Jan 13, 2010 at 02:13:42PM +0100, Peter Zijlstra wrote:
> On Wed, 2010-01-13 at 10:32 +0100, Ingo Molnar wrote:
> > other architectures have NMI concepts as well, such as Sparc64. 
> 
> I think both sparc64 and ppc64 fake NMIs by playing games with hw IRQ
> priorities and partial masks. But yes.
> 
> One interesting 'feature' for the perf-nmi interaction is creating an
> idle scheduling class for counters, because as long as there is a
> counter present you can use his NMIs to drive the watchdog, but as soon
> as there are non left, you need to install one.

Interesting idea.  How can I guarantee the frequency of the NMI I want to
piggyback off of?  A breakpoint that takes an hour to trigger may not be
the best NMI to use?  Then again I am still trying to understand the perf
event code a little better.

Cheers,
Don
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