On Fri, Aug 30, 2013 at 5:54 AM, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > On Thu, Aug 29, 2013 at 8:12 PM, Waiman Long <waiman.long@xxxxxx> wrote: >> On 08/29/2013 07:42 PM, Linus Torvalds wrote: >>> >>> Waiman? Mind looking at this and testing? Linus >> >> Sure, I will try out the patch tomorrow morning and see how it works out for >> my test case. > > Ok, thanks, please use this slightly updated patch attached here. > > It improves on the previous version in actually handling the > "unlazy_walk()" case with native lockref handling, which means that > one other not entirely odd case (symlink traversal) avoids the d_lock > contention. > > It also refactored the __d_rcu_to_refcount() to be more readable, and > adds a big comment about what the heck is going on. The old code was > clever, but I suspect not very many people could possibly understand > what it actually did. Plus it used nested spinlocks because it wanted > to avoid checking the sequence count twice. Which is stupid, since > nesting locks is how you get really bad contention, and the sequence > count check is really cheap anyway. Plus the nesting *really* didn't > work with the whole lockref model. > > With this, my stupid thread-lookup thing doesn't show any spinlock > contention even for the "look up symlink" case. > > It also avoids the unnecessary aligned u64 for when we don't actually > use cmpxchg at all. > > It's still one single patch, since I was working on lots of small > cleanups. I think it's pretty close to done now (assuming your testing > shows it performs fine - the powerpc numbers are promising, though), > so I'll split it up into proper chunks rather than random commit > points. But I'm done for today at least. > > NOTE NOTE NOTE! My test coverage really has been pretty pitiful. You > may hit cases I didn't test. I think it should be *stable*, but maybe > there's some other d_lock case that your tuned waiting hid, and that > my "fastpath only for unlocked case" version ends up having problems > with. > Following this thread with half an eye... Was that "unsigned" stuff fixed (someone pointed to it). How do you call that test-patch (subject)? I would like to test it on my SNB ultrabook with your test-case script. - Sedat - -- 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
