I confirmed that the underlying block devices (SAS, NVME) perform the same on the 4.4 and 4.15 kernels. Roughly 170 IOP/s direct to the SAS device and 570 IOP/s direct to the bcache infront of the SAS device. The block scheduler has no effect, due to the use of O_DIRECT. I can reproduce the sysbench difference in performance on 4.15 versus 4.4. The tuning helps though, only disabling sequential_cutoff really matters as this enables bcache to also cache reads; in general the faster reads allow additional writes. During testing, I believe the core issue we're seeing between 4.4 and 4.15 is around two things: 1) ext4 fs on bionic + enable metadata_csum by default on the filesystems, which will result in additional latency and IO as the csum is calculated and then embedded into the journal 2) fsync performance on 4.15 is measurably slower than on 4.4, even without csum_metadata enabled
-- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1806015 Title: bcache: performance regression without tuning under bionic To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1806015/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs