On Tue, 08 Oct 2013 12:25:05 +0200 Peter Zijlstra <[email protected]> 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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