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Date: Fri, 1 May 2015 12:14:53 +0200 From: Peter Zijlstra <peterz@...radead.org> To: Waiman Long <Waiman.Long@...com> Cc: Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org, Jason Low <jason.low2@...com>, Davidlohr Bueso <dave@...olabs.net>, Scott J Norton <scott.norton@...com>, Douglas Hatch <doug.hatch@...com> Subject: Re: [PATCH v4 1/2] locking/rwsem: reduce spinlock contention in wakeup after up_read/up_write On Thu, Apr 30, 2015 at 05:12:16PM -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@...com> > Suggested-by: Peter Zijlstra (Intel) <peterz@...radead.org> > --- Thanks! -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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