Messages in this thread | | | Date | Wed, 9 Oct 2013 22:50:06 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH 0/6] Optimize the cpu hotplug locking -v2 |
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On Tue, 08 Oct 2013 12:25:05 +0200 Peter Zijlstra <peterz@infradead.org> wrote:
> The current cpu hotplug lock is a single global lock; therefore excluding > hotplug is a very expensive proposition even though it is rare occurrence under > normal operation. > > There is a desire for a more light weight implementation of > {get,put}_online_cpus() from both the NUMA scheduling as well as the -RT side. > > The current hotplug lock is a full reader preference lock -- and thus supports > reader recursion. However since we're making the read side lock much cheaper it > is the expectation that it will also be used far more. Which in turn would lead > to writer starvation. > > Therefore the new lock proposed is completely fair; albeit somewhat expensive > on the write side. This in turn means that we need a per-task nesting count to > support reader recursion.
This is a lot of code and a lot of new complexity. It needs some pretty convincing performance numbers to justify its inclusion, no?
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