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Date: Mon, 12 Aug 2013 10:51:43 -0700
From: "H. Peter Anvin" <hpa@zytor.com>
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To: Linus Torvalds <torvalds@linux-foundation.org>
CC: Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Mike Galbraith <bitbucket@online.de>, Andi Kleen <ak@linux.intel.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [RFC] per-cpu preempt_count
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On 08/12/2013 10:35 AM, Linus Torvalds wrote:
> 
> Agreed. Making it atomic would suck, and cancel all advantages of the
> better code generation to access it. Good point.
> 
> And yeah, it could be two variables in the same cacheline or something.
> 

So we would have code looking something like:

	decl %fs:preempt_count
	jnz 1f
	cmpb $0,%fs:need_resched
	je 1f
	call __preempt_schedule
1:

It's a nontrivial amount of code, but would seem a fair bit better than
what we have now, at least.

	-hpa