Messages in this thread | | | Subject | Re: [PATCH v4 1/2] locking/rwsem: reduce spinlock contention in wakeup after up_read/up_write | From | Jason Low <> | Date | Thu, 30 Apr 2015 14:21:12 -0700 |
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On Thu, 2015-04-30 at 17:12 -0400, Waiman Long wrote: > In up_write()/up_read(), rwsem_wake() will be called whenever it > detects that some writers/readers are waiting. The rwsem_wake() > function will take the wait_lock and call __rwsem_do_wake() to do the > real wakeup. For a heavily contended rwsem, doing a spin_lock() on > wait_lock will cause further contention on the heavily contended rwsem > cacheline resulting in delay in the completion of the up_read/up_write > operations. > > This patch makes the wait_lock taking and the call to __rwsem_do_wake() > optional if at least one spinning writer is present. The spinning > writer will be able to take the rwsem and call rwsem_wake() later > when it calls up_write(). With the presence of a spinning writer, > rwsem_wake() will now try to acquire the lock using trylock. If that > fails, it will just quit. > > Signed-off-by: Waiman Long <Waiman.Long@hp.com> > Suggested-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Jason Low <jason.low2@hp.com>
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