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SubjectRe: [RFC] per-cpu preempt_count

* 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


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