linux-kernel - Re: [RFC 1/3] Unified NMI delayed call mechanism

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Date:	Fri, 18 Jun 2010 11:48:38 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>
Cc:	Huang Ying <ying.huang@...el.com>,
	Fr??d??ric Weisbecker <fweisbec@...il.com>,
	Don Zickus <dzickus@...hat.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
	Andi Kleen <andi@...stfloor.org>
Subject: Re: [RFC 1/3] Unified NMI delayed call mechanism


* Hidetoshi Seto <seto.hidetoshi@...fujitsu.com> wrote:

> (2010/06/12 19:25), Ingo Molnar wrote:
> > 
> > * Huang Ying <ying.huang@...el.com> wrote:
> > 
> >> NMI can be triggered even when IRQ is masked. So it is not safe for NMI 
> >> handler to call some functions. One solution is to delay the call via self 
> >> interrupt, so that the delayed call can be done once the interrupt is 
> >> enabled again. This has been implemented in MCE and perf event. This patch 
> >> provides a unified version and make it easier for other NMI semantic handler 
> >> to take use of the delayed call.
> > 
> > Instead of introducing this extra intermediate facility please use the same 
> > approach the unified NMI watchdog is using (see latest -tip): a perf event 
> > callback gives all the extra functionality needed.
> > 
> > The MCE code needs to be updated to use that - and then it will be integrated 
> > into the events framework.
> 
> Hi Ingo,
> 
> I think this "NMI delayed call mechanism" could be a part of "the events 
> framework" that we are planning to get in kernel soon. [...]

My request was to make it part of perf events - which is a generic event 
logging framework. We dont really need/want a second 'events framework'
as we have one already ;-)

> [...]  At least APEI will use NMI to report some hardware events (likely 
> error) to kernel.  So I suppose we will go to have a delayed call as an 
> event handler for APEI.

Yep, that makes sense. I wasnt arguing against the functionality itself, i was 
arguing against the illogical layering that limits its utility. By making it 
part of perf events it becomes a generic part of that framework and can be 
used by anything that deals with events and uses that framework.

Thanks,

	Ingo
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