On Wed, Feb 10, 2021 at 12:18:53PM +0000, Michal Rostecki wrote: > > These patches look good. But as only round-robin policy requires > > to monitor the inflight and last-offset. Could you bring them under > > if policy=roundrobin? Otherwise, it is just a waste of CPU cycles > > if the policy != roundrobin. > > > > If I bring those stats under if policy=roundrobin, they are going to be > inaccurate if someone switches policies on the running system, after > doing any I/O in that filesystem. > > I'm open to suggestions how can I make those stats as lightweight as > possible. Unfortunately, I don't think I can store the last physical > location without atomic_t. > > The BIO percpu counter is probably the least to be worried about, though > I could maybe get rid of it entirely in favor of using part_stat_read(). >
Actually, after thinking about that more, I'm wondering if I should just drop the last-offset stat and penalty mechanism entirely. They seem to improve performance slightly only on mixed workloads (thought I need to check if that's the case in all-SDD od all NVMe arrays), but still perform worse than policies that you proposed. Maybe it'd be better if I just focus on getting the best performance on non-mixed environments in my policy and thus stick to the simple `inflight < queue_depth` check... Thanks, Michal
