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SubjectRe: smp: Start up non-boot CPUs asynchronously
On Tue, 31 Jan 2012 15:31:31 +0100
Ingo Molnar <mingo@elte.hu> wrote:

> >
> > by inspection, anything that calls
> > get_online_cpus()/put_online_cpus() will block while a CPU is
> > coming up. This is used in things like kmem_cache_create()...
> > which is used about everywhere. (there's various other
> > places... more or less it's a requirement for using the
> > for_each_online_cpu() api correctly)
>
> Still magic delays are not acceptable - we want to face any
> remaining performance problems head on, we want to understand
> and fix them correctly.

it's not really a performance problem as it is an obvious "we have a
ton of back-to-back writers on a read-write lock that we have quite a
few readers for". Unless the writers back off a little, the readers are
going to get starved.


--
Arjan van de Ven Intel Open Source Technology Centre
For development, discussion and tips for power savings,
visit http://www.lesswatts.org


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