Re: PATCH: Fix race in cpu_down (hotplug cpu)

Nick Piggin
2005-09-19T07:37:18Z

On Mon, 2005-09-19 at 09:28 +0200, Ingo Molnar wrote:
> * Nick Piggin <nickpiggin@yahoo.com.au> wrote:

> > Oh really? I think yes, the latency should be taken care of because we
> > want to be able to provide good latency even for !preempt kernels. If
> > a solution can be found for acpi_processor_idle, that would be ideal.
>
> the ACPI idle code runs with irqs disabled anyway, so there's no issue
> here. If something takes long there, we can do little about it. (but in
> practice ACPI sleep latencies are pretty ok - the only latencies i found
> in the past were due to need_resched bugs in the ACPI idle routine)
>

Ah, in that case I agree: we have nothing to worry about by merging
such a patch then.

> > IMO it always felt kind of hackish to run the idle threads with
> > preempt on.
>
> Yes, idle threads can have preemption disabled. There's not any big
> difference in terms of latencies, the execution paths are all very
> short.
>

Thanks for the confirmation Ingo. This is part of my "cleanup resched
and cpu_idle" patch FYI. It should already be in -mm, but has some
trivial EM64T bug in it that Andrew hits but I can't reproduce.

I'll dust it off and send it out, hopefully someone will be able to
reproduce the problem!

--
SUSE Labs, Novell Inc.

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