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Date: Thu, 24 Oct 2002 10:36:22 -0500
From: Corey Minyard <cminyard@mvista.com>
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To: John Levon <levon@movementarian.org>
CC: dipankar@gamebox.net, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] NMI request/release, version 5 - I think this one's ready
References: <20021022233853.B25716@dikhow> <3DB59923.9050002@mvista.com> <20021022190818.GA84745@compsoc.man.ac.uk> <3DB5C4F3.5030102@mvista.com> <20021023230327.A27020@dikhow> <3DB6E45F.5010402@mvista.com> <20021024002741.A27739@dikhow> <3DB7033C.1090807@mvista.com> <20021024132004.A29039@dikhow> <3DB7F574.9030607@mvista.com> <20021024144632.GC32181@compsoc.man.ac.uk>
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John Levon wrote:

>On Thu, Oct 24, 2002 at 08:28:20AM -0500, Corey Minyard wrote:
>
>  
>
>>diff -ur linux.orig/arch/i386/kernel/traps.c linux/arch/i386/kernel/traps.c
>>--- linux.orig/arch/i386/kernel/traps.c	Mon Oct 21 13:25:45 2002
>>+++ linux/arch/i386/kernel/traps.c	Thu Oct 24 08:11:14 2002
>>    
>>
>
>At this point I'd quite like to see :
>
>	mv nmi.c nmi_watchdog.c
>
>and put all this stuff in always-compiled nmi.c.  traps.c is getting
>bloated.
>
I agree.

>
>  
>
>> static void default_do_nmi(struct pt_regs * regs)
>> {
>> 	unsigned char reason = inb(0x61);
>>  
>> 	if (!(reason & 0xc0)) {
>>-#if CONFIG_X86_LOCAL_APIC
>> 		/*
>>-		 * Ok, so this is none of the documented NMI sources,
>>-		 * so it must be the NMI watchdog.
>>+		 * Check the handler list to see if anyone can handle this
>>+		 * nmi.
>> 		 */
>>-		if (nmi_watchdog) {
>>-			nmi_watchdog_tick(regs);
>>+		if (call_nmi_handlers(regs))
>>    
>>
>
>Now you're using RCU, it's a real pity that we have the inb() first -
>if it wasn't for that, there would be no reason at all to have the "fast
>path" setting code too (the latter code is ugly, which is one reason I
>want to ditch it).
>
>How about adding default_do_nmi as the minimal-priority handler, then
>add the watchdog with higher priority above that ? Then oprofile can add
>itself on top of those both and return NOTIFY_OK to indicate it should
>break out of the loop. As a bonus, you lose the inb() for the watchdog
>too.
>
Is there any way to detect if the nmi watchdog actually caused the 
timeout?  I don't understand the hardware well enough to do it without 
some work, but it would be a VERY good idea to make sure the nmi 
watchdog actully caused the operation.

Plus, can't you get more than one cause of an NMI?  Shouldn't you check 
them all?

>>+++ linux/include/asm-i386/irq.h	Wed Oct 23 16:47:24 2002
>>    
>>
>
>I thought you agreed the stuff should be in asm/nmi.h ?
>
I will (I had forgotten), and I will move nmi.h to nmi_watchdog.h.

-Corey

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