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Date: Tue, 13 Aug 2013 17:56:37 +0200
From: Ingo Molnar <mingo@kernel.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Mike Galbraith <bitbucket@online.de>, Peter Anvin <hpa@zytor.com>,
        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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* Linus Torvalds <torvalds@linux-foundation.org> wrote:

> On Tue, Aug 13, 2013 at 5:26 AM, Peter Zijlstra <peterz@infradead.org> wrote:
> >
> > So we're now down to something like:
> >
> >   decl fs:preempt_count
> >   cmpl PREEMPT_NEED_RESCHED,fs:preempt_count
> >   jnz 1f
> 
> Well, this isn't worth doing unless you can make PREEMPT_NEED_RESCHED be 
> the high bit, and we can combine it into just "decl+jns". Otherwise we'd 
> be better off with the simpler two separate adjacent variables.

Definitely, the cmpl should be avoided.

PREEMPT_NEED_RESCHED could be made the high bit - or maybe an even simpler 
solution is to invert its meaning: making '0' the "it needs to resched!" 
case, so the check would be decl+jz?

Thanks,

	Ingo