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

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Date:	Fri, 18 Jun 2010 23:16:23 +0800
From:	huang ying <huang.ying.caritas@...il.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>,
	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

On Fri, Jun 18, 2010 at 10:35 PM, Ingo Molnar <mingo@...e.hu> wrote:
>
> * huang ying <huang.ying.caritas@...il.com> wrote:
>
>> On Fri, Jun 18, 2010 at 8:45 PM, Ingo Molnar <mingo@...e.hu> wrote:
>> >> >> [...] ??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.
>> >>
>> >> I think the the 'layering' in the patchset helps instead of 'limits' its
>> >> utility. It is designed to be as general as possible, so that it can be used
>> >> by both perf and other NMI users. Do you think so?
>> >
>> > What other NMI users do you mean? EDAC/MCE is going to go utilize events
>> > as well (away from the horrible /dev/mcelog interface), the NMI watchdog
>> > already did it and the perf tool obviously does as well. There's a few
>> > leftovers like kcrash which isnt really event centric and i dont think it
>> > needs to be converted.
>>
>> But why not just make it more general? It does not hurt anyone including
>> perf.
>
> Because it's not actually more generic that way - just look at the code. It's
> x86 specific, plus it ties it to NMI delivery while the concept of delayed
> execution has nothing to do with NMIs.

soft_irq is a delayed mechanism for IRQ, a self interrupt can be a
delayed mechanism for NMI. If we can make soft_irq NMI-safe, we can
use soft_irq as a backup of self interrupt (for systems without APIC
and maybe for other architectures).

Best Regards,
Huang Ying
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