On Wed, 2012-10-17 at 15:25 -0500, Nathan Zimmer wrote: > I am currently tracking a hotlock reported by a customer on a large, 512 cores, > system, I am currently running 3.7.0 rc1 but the issue looks like it has been > this way for a very long time. > The offending lock is proc_dir_entry->pde_unload_lock. > > This patch converts the replaces the lock with the rcu. It is a refresh of what > was orignally suggested by Eric Dumazet. I refreshed it to the 3.7. > > Supporting numbers, lower is better, they are from the test I posted earlier. > cpuinfo baseline Rcu > tasks read-sec read-sec > 1 0.0141 0.0141 > 2 0.0140 0.0142 > 4 0.0140 0.0141 > 8 0.0145 0.0140 > 16 0.0553 0.0168 > 32 0.1688 0.0549 > 64 0.5017 0.1690 > 128 1.7005 0.5038 > 256 5.2513 2.0804 > 512 8.0529 3.0162 > > > Cc: Eric Dumazet <eric.dumazet@xxxxxxxxx> > Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx> > Cc: David Woodhouse <dwmw2@xxxxxxxxxxxxx> > Cc: Alexey Dobriyan <adobriyan@xxxxxxxxx> > Signed-off-by: Nathan Zimmer <nzimmer@xxxxxxx> Hmm, this patch had several issues and I had no time yet to work on a new version. I probably wont have time in a near future. Paul sent me some comments about it, I hope he doesnt mind I copy them here, if you want to polish the patch. Thanks ! On Wed, 2012-10-03 at 10:56 -0700, Paul E. McKenney wrote: > Finally getting back to this... :-/ > > Why not set the initial value of the reference counter to 1 > (rather than zero), continue acquiring with atomic_inc(), but > use atomic_dec_and_test() to decrement? Put a completion in > the data structure, so if the atomic_dec_and_test() indicates that > the counter is now zero, do a complete(). > > Then to free the object, remove it from the data structure, do a > synchronize_rcu(), do an atomic_dec_and_test() to remove the initial > value, again doing a complete() if the counter is now zero. The do > a wait_for_completion(). > > This would get rid of the polling loop. > > So, what am I missing here? ;-) > > Thanx, Paul > -- 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
