Messages in this thread | | | Date | Tue, 03 May 2005 09:23:19 +1000 | From | Nick Piggin <> | Subject | Re: [RFC PATCH] Dynamic sched domains (v0.5) |
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Dinakar Guniguntala wrote: > On Mon, May 02, 2005 at 07:44:05PM +1000, Nick Piggin wrote: > >>Dinakar Guniguntala wrote: >> >> >>>+void rebuild_sched_domains(cpumask_t span1, cpumask_t span2) >>>+{ >>>+ cpumask_t change_map; >>>+ >>>+ cpus_or(change_map, span1, span2); >>>+ >>>+ preempt_disable(); >> >>Oh, you can't do this here, attach_domains does a synchronize_kernel. >>So take it out, it doesn't do anything anyway, does it? > > > I put that in to prevent hangs with CONFIG_PREEMPT turned on, but > clearly didn't test it with preempt turned on. Looks like all I need to > do here is a local_irq_disable >
What are you protecting against, though? synchroinze_kernel can sleep, so local_irq_disable is probably the wrong thing to do as well.
AFAIKS, you don't need anything here - so long as you have mutual exclusion from other sched-domain building then this can take as long as it wants / be preempted as many times as we like.
> >>I suggest you also use some sort of locking to prevent concurrent rebuilds >>and rebuilds racing with cpu hotplug. You could probably have a static >>semaphore around rebuild_sched_domains, and take lock_cpu_hotplug here too. > > > I already do a lock_cpu_hotplug() in cpuset.c before calling > rebuild_sched_domains and also am holding cpuset_sem, so that should take > care of both hotplug and concurrent rebuilds >
OK.
But if we want this to be a respectable interface (possibly for more than just cpusets) then it should probably do some locking itself. It isn't performance critical, so I think taking a semaphore wouldn't hurt.
-- SUSE Labs, Novell Inc.
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