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From: Mikael Pettersson <mikpe@csd.uu.se>
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Date: Fri, 2 Feb 2001 17:28:26 +0100
To: "Maciej W. Rozycki" <macro@ds2.pg.gda.pl>
Cc: Mikael Pettersson <mikpe@csd.uu.se>, alan@lxorguk.ukuu.org.uk,
        linux-kernel@vger.kernel.org, mingo@elte.hu
Subject: Re: [PATCH] 2.4.1-ac1 UP-APIC/NMI watchdog fixes
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Maciej W. Rozycki writes:
 >  I've forgotten to cc you when sending Ingo my patch-2.4.0-ac12-upapic-19
 > fixes a few days ago, my apologies.  Since the two patches conflict with
 > each other, I've merged them together and provide the result below. 
 > Please check if it is fine for you. 

Looks fine to me.

 >  I'm unsure about the K7_NMI_EVENT macro -- I think it should go into
 > include/asm-i386/msr.h, but the comment should remain here.  It should get
 > reworded a bit in this case, I suppose, though. 

I'd prefer to keep it in nmi.c -- it doesn't really have any relevance
elsewhere. I made a macro of it so that I wouldn't need any #ifdef:s
or long explanations in the code proper.

There is one thing which bothers me. Look at the end of the NMI handler:

 > +	if (cpu_has_apic && (nmi_watchdog == NMI_LOCAL_APIC))
 > +		wrmsr(nmi_perfctr_msr, -(cpu_khz/HZ*1000), -1);

This becomes a series of loads and tests. Ideally, a _single_ test should suffice
to inform the NMI handler whether we're in NMI_LOCAL_APIC mode or not. One problem
is that we aren't resetting nmi_watchdog to NMI_NONE if we fail to detect or
initialise the local APIC; if we did, we could kill the cpu_has_apic test.

... however, nmi_perfctr_msr could serve this purpose since it will be
non-zero if and only if (cpu_has_apic && nmi_watchdog == NMI_LOCAL_APIC).
So I would actually suggest something like:

	if (nmi_perfctr_msr)
		wrmsr(nmi_perfctr_msr, -(cpu_khz/HZ*1000), -1);

/Mikael
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