On Fri, Jun 03, 2016 at 02:33:47PM +1000, Benjamin Herrenschmidt wrote: > - For the above, can you show (or describe) where the qspinlock > improves things compared to our current locks. So currently PPC has a fairly straight forward test-and-set spinlock IIRC. You have this because LPAR/virt muck and lock holder preemption issues etc.. qspinlock is 1) a fair lock (like ticket locks) and 2) provides out-of-word spinning, reducing cacheline pressure. Esp. on multi-socket x86 we saw the out-of-word spinning being a big win over our ticket locks. And fairness, brought to us by the ticket locks a long time ago, eliminated starvation issues we had, where a spinner local to the holder would 'always' win from a spinner further away. So under heavy enough local contention, the spinners on 'remote' CPUs would 'never' get to own the lock. pv-qspinlock tries to preserve the fairness while allowing limited lock stealing and explicitly managing which vcpus to wake. > While there's > theory and to some extent practice on x86, it would be nice to > validate the effects on POWER. Right; so that will have to be from benchmarks which I cannot help you with ;-) _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
