On Wed, 2011-01-05 at 11:39 +0900, KOSAKI Motohiro wrote: > After calling pthread_cond_signal(), T1 which cond_signal caller and T2 > which waked start to GIL grab race. But usually T1 is always win because > lock variable is in T1's cpu cache. Why kernel and userland have so much > different result? One of a reason is glibc doesn't have any ticket lock scheme. The problem is that making locks strictly fair is that that sucks for performance, iirc most futex ops are fifo-ordered when they his the block path, but we do allow for lock-stealing. Lock-stealing greatly improves performance since it avoids lots of block/wakeup cycles, but it does make things unfair. I'm not sure we have a futex option to disable lock-stealing, nor do I think you really want to, performance suffers really badly. [This btw is the reason why people reported a performance improvement when they wrapped all mmap() calls in a pthread_mutex, the rwsem_down_write() thing doesn't allow for lock-stealing since it needs to be strict fifo-fair] -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
