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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
Date: Tue, 13 Aug 2013 17:56:37 +0200	[thread overview]
Message-ID: <20130813155637.GA5280@gmail.com> (raw)
In-Reply-To: <CA+55aFxieQGUkEi9i=LRzVK2DRvavKgF-YEvskvJhF3-5xiU2A@mail.gmail.com>


* 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

  reply	other threads:[~2013-08-13 15:56 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-08-12 11:51 [RFC] per-cpu preempt_count Peter Zijlstra
2013-08-12 17:35 ` Linus Torvalds
2013-08-12 17:51   ` H. Peter Anvin
2013-08-12 18:53     ` Linus Torvalds
2013-08-13  8:39       ` Peter Zijlstra
2013-08-12 17:58   ` Ingo Molnar
2013-08-12 19:00     ` Linus Torvalds
2013-08-12 20:44       ` H. Peter Anvin
2013-08-13 10:30       ` Ingo Molnar
2013-08-13 12:26         ` Peter Zijlstra
2013-08-13 15:39           ` Linus Torvalds
2013-08-13 15:56             ` Ingo Molnar [this message]
2013-08-13 16:26               ` Peter Zijlstra
2013-08-13 16:28               ` H. Peter Anvin
2013-08-13 16:29             ` Peter Zijlstra
2013-08-13 16:38               ` Linus Torvalds
2013-08-18 17:57   ` Paul E. McKenney

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