On Thu, Aug 3, 2017 at 6:47 PM, Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> wrote: > On Thu, Aug 03, 2017 at 05:57:50PM +0800, Ming Lei wrote: >> On Thu, Aug 3, 2017 at 5:42 PM, Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> wrote: >> > On Thu, Aug 03, 2017 at 05:17:21PM +0800, Ming Lei wrote: >> >> Hi Mel Gorman, >> >> >> >> On Thu, Aug 3, 2017 at 4:51 PM, Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> wrote: >> >> > Hi Christoph, >> >> > >> >> > I know the reasons for switching to MQ by default but just be aware that it's >> >> > not without hazards albeit it the biggest issues I've seen are switching >> >> > CFQ to BFQ. On my home grid, there is some experimental automatic testing >> >> > running every few weeks searching for regressions. Yesterday, it noticed >> >> > that creating some work files for a postgres simulator called pgioperf >> >> > was 38.33% slower and it auto-bisected to the switch to MQ. This is just >> >> > linearly writing two files for testing on another benchmark and is not >> >> > remarkable. The relevant part of the report is >> >> >> >> We saw some SCSI-MQ performance issue too, please see if the following >> >> patchset fixes your issue: >> >> >> >> http://marc.info/?l=linux-block&m=150151989915776&w=2 >> >> >> > >> > That series is dealing with problems with legacy-deadline vs mq-none where >> > as the bulk of the problems reported in this mail are related to >> > legacy-CFQ vs mq-BFQ. >> >> The serials deals with none and all mq schedulers, and you can see >> the improvement on mq-deadline in cover letter, :-) >> > > Would it be expected to fix a 2x to 4x slowdown as experienced by BFQ > that was not observed on other schedulers? Actually if you look at the cover letter, you will see this patchset increases by > 10X sequential I/O IOPS on mq-deadline, so it would be reasonable to see 2x to 4x BFQ slowdown, but I didn't test BFQ. Thanks, Ming Lei
