Messages in this thread | | | Date | Mon, 12 Aug 2013 11:53:25 -0700 | Subject | Re: [RFC] per-cpu preempt_count | From | Linus Torvalds <> |
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On Mon, Aug 12, 2013 at 10:51 AM, H. Peter Anvin <hpa@zytor.com> wrote: > > 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.
Well, we currently don't even bother checking the preempt count at all, and we just optimistically assume that we don't nest in the common case. The preempt count is then re-checked in __preempt_schedule, I think.
Which sounds like a fair approach.
So the code would be simplified to just
decl %fs:preempt_count cmpb $0,%fs:need_resched jne .. unlikely branch that calls __preempt_schedule
which is not horrible. Not *quite* as nice as just doing a single "decl+js", but hey, certainly better than what we have now.
Linus
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