On 9/28/18 11:45 AM, Josef Bacik wrote: > v1->v2: > - rebased onto a recent for-4.20/block branch > - dropped the changed variable cleanup. > > -- Original message -- > > Testing on ssd's with the current iolatency code wasn't working quite as well. > This is mostly because ssd's don't behave like rotational drives, they are more > spikey which means that using the average latency for IO wasn't very responsive > until the drive was extremely over taxed. To deal with this I've reworked > iolatency to use a p(90) based approach for ssd latencies. I originally > intended to use this approach for both ssd's and rotational drives, but p(90) > was too high of a bar to use. By the time we were exceeding p(90) things were > already pretty bad. So to keep things simpler just use p(90) for ssd's since > their latency targets tend to be orders of magnitude lower than rotational > drives, and keep the average latency calculations for rotational drives. > > This testing also showed a few issues with blk-iolatency, so the preceding > patches are all fixing issues we saw in testing. Using q->nr_requests instead > of blk_queue_depth() is probably the most subtle and important change. We want > to limit the IO's based on the number of outstanding requests we can have in the > block layer, not necessarily how many we can have going to the device. So make > this explicity by using nr_requests directly. These patches have been in > production for a week on both our rotational and ssd tiers and everything is > going smoothly. Thanks, Applied for 4.20, thanks for respinning. -- Jens Axboe
