Re: [RFC] per-cpu preempt_count

[Ingo Molnar]

* Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:

> On Tue, Aug 13, 2013 at 5:26 AM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> 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
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