linux-kernel - Re: [RFC] Avoid PIT SMP lockups

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Message-Id: <200610170040.49502.ak@suse.de>
Date:	Tue, 17 Oct 2006 00:40:49 +0200
From:	Andi Kleen <ak@...e.de>
To:	Zachary Amsden <zach@...are.com>
Cc:	caglar@...dus.org.tr, Gerd Hoffmann <kraxel@...e.de>,
	john stultz <johnstul@...ibm.com>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] Avoid PIT SMP lockups

> It might only happen with SMP because the difficulty of getting good 
> enough TSC / timer IRQ synchronization during boot increases 
> exponentially with SMP configurations. And it might pass 10% of the time 
> because you were lucky enough not to fire off another timer interrupt yet.

We have the same problem with NMI watchdog events unfortunately. 
Need to call something in the nmi watchdog code to make sure it is 
not renewed and then reenabled.
Or maybe it's better to figure out a way that yields atomic patches.

I think the best way is to make sure all alternative() patches
are always done before the code can be ever executed - this
means doing it very early for the main kernel. The only exception
would be the LOCK prefix patching, which should be atomic.

iirc there was some more patching except lock prefixes going on for 
SMP<->UP transisitions,  but last time I checked they didn't look 
particularly useful and could be probably eliminated.

-Andi
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