linux-kernel - Re: [PATCH -v3 3/6] x86, NMI, Rewrite NMI handler

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Message-ID: <1286864080.7768.179.camel@yhuang-dev>
Date:	Tue, 12 Oct 2010 14:14:40 +0800
From:	Huang Ying <ying.huang@...el.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Don Zickus <dzickus@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	"H. Peter Anvin" <hpa@...or.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andi Kleen <andi@...stfloor.org>,
	Robert Richter <robert.richter@....com>
Subject: Re: [PATCH -v3 3/6] x86, NMI, Rewrite NMI handler

On Tue, 2010-10-12 at 14:04 +0800, Peter Zijlstra wrote:
> On Tue, 2010-10-12 at 08:50 +0800, Huang Ying wrote:
> > On Tue, 2010-10-12 at 00:13 +0800, Peter Zijlstra wrote:
> > > On Sat, 2010-10-09 at 14:49 +0800, Huang Ying wrote:
> > > > notify_die(DIE_NMI_IPI);
> > > > notify_die(DIE_NMI);
> > > > /* process io port 0x61 */
> > > > nmi_watchdog_touch();
> > > > unknown_nmi(); 
> > > 
> > > Why keep NMI_IPI? What the heck is it for?
> > 
> > DIE_NMI_IPI is used for CPU-specific or CPU-local NMIs, such as perf
> > NMI. While DIE_NMI is used for non-CPU-specific or global NMIs, such as
> > NMI notification from source bridge.
> > 
> > The order between these two is important. So we use two die value to
> > enforce the order.
> 
> But you can't know about that, there is no reason field to distinguish
> between these cases, so you might as well fold it into a single notifier
> chain and be done with it.

NMI users know that. Such as perf uses CPU-specific NMI, while APEI GHES
uses non-CPU-specific NMI. Different users expect different die values,
such as perf expects DIE_NMI_IPI, while APEI GHES expects DIE_NMI, so
that perf can be checked before APEI GHES.

> There is no good reason to call two chains when one is enough.
> 
> Also, the IPI name is terrible, its not IPI related at all. Please kill
> the thing.

I agree with you that IPI is not a good name. Can you suggest a better
name?

Best Regards,
Huang Ying


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