2016-07-11 22:44 GMT+02:00 Jon Bernard <jbernard@xxxxxxxxxx>: > Greetings, > > I have recently noticed a large difference in performance between thick > and thin LVM volumes and I'm trying to understand why that it the case. > > In summary, for the same FIO test (attached), I'm seeing 560k iops on a > thick volume vs. 200k iops for a thin volume and these results are > pretty consistent across different runs. > > I noticed that if I run two FIO tests simultaneously on 2 separate thin > pools, I net nearly double the performance of a single pool. And two > tests on thin volumes within the same pool will split the maximum iops > of the single pool (essentially half). And I see similar results from > linux 3.10 and 4.6. > > I understand that thin must track metadata as part of its design and so > some additional overhead is to be expected, but I'm wondering if we can > narrow the gap a bit. > > In case it helps, I also enabled LOCK_STAT and gathered locking > statistics for both thick and thin runs (attached). > > I'm curious to know whether this is a know issue, and if I can do > anything the help improve the situation. I wonder if the use of the > primary spinlock in the pool structure could be improved - the lock > statistics appear to indicate a significant amount of time contending > with that one. Or maybe it's something else entirely, and in that case > please enlighten me. > > If there are any specific questions or tests I can run, I'm happy to do > so. Let me know how I can help. > > -- > Jon Hi Jon, Have you try to enable scsi_mq mode in newer kernel eg 4.6, see if it makes any difference? Regards, Jack > > -- > dm-devel mailing list > dm-devel@xxxxxxxxxx > https://www.redhat.com/mailman/listinfo/dm-devel -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
