linux-kernel - Re: nmi_watchdog fix for x86

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Message-Id: <200710012341.53169.ak@suse.de>
Date:	Mon, 1 Oct 2007 23:41:52 +0200
From:	Andi Kleen <ak@...e.de>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Arjan van de Ven <arjan@...radead.org>,
	David Bahi <dbahi@...ell.com>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-rt-users@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Gregory Haskins <GHaskins@...ell.com>
Subject: Re: nmi_watchdog fix for x86_64 to be more like i386


> IRQ_NOBALANCING is not preventing cpu unplug. It moves the affinity to the
> next CPU, but the check in NMI watchdog for CPU == 0 would not longer
> work.

That cannot happen right now because cpu_disable() on both i386/x86-64
reject CPU #0. So just setting IRQ_NOBALANCING is sufficient and both
do that already. I was wrong earlier in being concerned about this.

>  int tick_do_broadcast(cpumask_t mask)
> @@ -137,6 +147,7 @@ int tick_do_broadcast(cpumask_t mask)
>  		cpu_clear(cpu, mask);
>  		td = &per_cpu(tick_cpu_device, cpu);
>  		td->evtdev->event_handler(td->evtdev);
> +		tick_broadcast_account(cpu);

That would not handle the case with a single CPU running only
irq  0 but not broadcasting I think.

I believe ftp://ftp.firstfloor.org/pub/ak/x86_64/quilt/patches/fix-watchdog
is the correct fix

-Andi
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