proposed smp_rendezvous change
Andriy Gapon
avg at FreeBSD.org
Sun May 15 07:12:52 UTC 2011
on 14/05/2011 18:25 John Baldwin said the following:
> Hmmm, so this is not actually sufficient. NetApp ran into a very similar race
> with virtual CPUs in BHyVe. In their case because virtual CPUs are threads that
> can be preempted, they have a chance at a longer race.
>
> The problem that they see is that even though the values have been updated, the
> next CPU to start a rendezvous can clear smp_rv_waiters[2] to zero before one of
> the other CPUs notices that it has finished.
As a follow up to my previous question. Have you noticed that in my patch no
slave CPU actually waits/spins on smp_rv_waiters[2]? It's always only master
CPU (and under smp_ipi_mtx).
--
Andriy Gapon
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