On Thu, 9 Apr 2009, Andi Kleen wrote: > > You have to be very careful with this. Mutexes can be slower than > spinlocks (and the new BKL is a spinlock) in some situations, they > typically schedule much more etc., which can be costly. Actually, with the new adaptive spinning, that basically shouldn't be true any more. Or rather, you should need some really bad/unlucky situation for it to scheduler more than necessary, and if the locker _acts_ like a spinlock (ie it doesn't block while holding the lock), performance should approach a spinlock. That said, there are definitely reasons why a mutex can be slower than the BKL, and the whole "BKL gets implicitly dropped at sleep time" is very high on that list of reasons. The sleeping patterns can be _very_ different with a mutex than with a BKL. > Better would be to use spinlocks if possible. I guess you just would > need to find all sleep points and wrap them with lock dropping? I do agree that a filesystem should try to avoid sleeping locks if at all possible, especially on the paths that the VM uses for writeback. But on the other hand, I think the issue with reiserfs is just the bad latencies that the BKL can cause, and then it doesn't matter. Linus -- To unsubscribe from this list: send the line "unsubscribe reiserfs-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
