Messages in this thread | | | Date | Wed, 7 Nov 2007 18:20:27 -0600 | From | Matt Mackall <> | Subject | Re: is minimum udelay() not respected in preemptible SMP kernel-2.6.23? |
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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).
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