Messages in this thread | | | Date | Thu, 08 Nov 2007 13:46:48 +0200 | From | Avi Kivity <> | Subject | Re: is minimum udelay() not respected in preemptible SMP kernel-2.6.23? |
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Andi Kleen wrote: > On Thursday 08 November 2007 01:20, Matt Mackall wrote: > >> On Wed, Nov 07, 2007 at 12:30:45PM -0800, Andrew Morton wrote: >> >>> Ow. Yes, from my reading delay_tsc() can return early (or after >>> heat-death-of-the-universe) if the TSCs are offset and if preemption >>> migrates the calling task between CPUs. >>> >>> I suppose a lameo fix would be to disable preemption in delay_tsc(). >>> >> preempt_disable is lousy documentation here. This and other cases >> (lots of per_cpu users, IIRC) actually want a migrate_disable() which >> is a proper subset. We can simply implement migrate_disable() as >> preempt_disable() for now and come back later and implement a proper >> migrate_disable() that still allows preemption (and thus avoids the >> latency). >> > > We could actually do this right now. migrate_disable() can be just changing > the cpu affinity of the current thread to current cpu and then restoring it > afterwards. That should even work from interrupt context. > > get_cpu() etc. could be changed to use this then too. > >
What if some other thread calls sched_setaffinity() on the migrate_disable()d cpu? we'd need to detect this to avoid migrate_enable() stomping on sched_setaffinity()'s work.
-- error compiling committee.c: too many arguments to function
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