linux-kernel - Re: introduce NMI_AUTO as nmi

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Message-ID: <20100113163551.GA10643@elte.hu>
Date:	Wed, 13 Jan 2010 17:35:51 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Don Zickus <dzickus@...hat.com>,
	Cyrill Gorcunov <gorcunov@...il.com>, aris@...hat.com,
	linux-kernel@...r.kernel.org
Subject: Re: introduce NMI_AUTO as nmi_watchdog option


* Peter Zijlstra <peterz@...radead.org> 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.

Yeah. I'd suggest to not complicate things with that initially - but to simply 
create a standalone event for it and 'waste' a counter on NMI generation. 

Later on it can indeed be a good feature to make the NMI watchdog 'seemless' 
in the sense of it not causing any wasted hw resources - it can piggyback on 
any existing NMI event. (as long as that event is at least ~1 HZ strong or so)

	Ingo
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