linux-kernel - Re: [RFC] per-cpu preempt

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Message-ID: <520920AF.1050407@zytor.com>
Date:	Mon, 12 Aug 2013 10:51:43 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Mike Galbraith <bitbucket@...ine.de>,
	Andi Kleen <ak@...ux.intel.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] per-cpu preempt_count

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

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