On Wed, Jan 14, 2009 at 05:46:39PM +0100, Peter Zijlstra wrote: > On Mon, 2009-01-12 at 19:32 +0200, Avi Kivity wrote: > > Peter Zijlstra wrote: > > > Spinlocks can use 'pure' MCS locks. > > > > > > > How about this, then. In mutex_lock(), keep wait_lock locked and only > > release it when scheduling out. Waiter spinning naturally follows. If > > spinlocks are cache friendly (are they today?) > > (no they're not, Nick's ticket locks still spin on a shared cacheline > IIRC -- the MCS locks mentioned could fix this) It reminds me. I wrote a basic variation of MCS spinlocks a while back. And converted dcache lock to use it, which showed large dbench improvements on a big machine (of course for different reasons than the dbench improvements in this threaed). http://lkml.org/lkml/2008/8/28/24 Each "lock" object is sane in size because given set of spin-local queues may only be used once per lock stack. But any spinlocks within a mutex acquisition will always be at the bottom of such a stack anyway, by definition. If you can use any code or concept for your code, that would be great. > > we inherit that. If > > there is no contention on the mutex, then we don't need to reacquire the > > wait_lock on mutex_unlock() (not that the atomic op is that expensive > > these days). > > That might actually work, although we'd have to move the > __mutex_slowpath_needs_to_unlock() branch outside wait_lock otherwise > we'll deadlock :-) > > It might be worth trying this if we get serious fairness issues with the > current construct. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
