On Mon, Aug 12, 2013 at 11:53:25AM -0700, Linus Torvalds wrote: > On Mon, Aug 12, 2013 at 10:51 AM, H. Peter Anvin <h...@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.
OK, so doing per-cpu need_resched is a trivial patch except for the mwait side of things. Then again, Arjan already asked for per-cpu need_resched specifically for mwait so we might as well do that. The only complication is that IIRC Arjan wants to stagger the mwait cache-lines and we would very much like our preempt_count and need_resched (and possible some other __switch_to related things) in the same cacheline. Afaict that'll yield a double indirect again :/ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
