On 05/03/2017 08:08 AM, Jens Axboe wrote: > On 05/02/2017 10:03 PM, Ming Lei wrote: >> On Fri, Apr 28, 2017 at 02:29:18PM -0600, Jens Axboe wrote: >>> On 04/28/2017 09:15 AM, Ming Lei wrote: >>>> Hi, >>>> >>>> This patchset introduces flag of BLK_MQ_F_SCHED_USE_HW_TAG and >>>> allows to use hardware tag directly for IO scheduling if the queue's >>>> depth is big enough. In this way, we can avoid to allocate extra tags >>>> and request pool for IO schedule, and the schedule tag allocation/release >>>> can be saved in I/O submit path. >>> >>> Ming, I like this approach, it's pretty clean. It'd be nice to have a >>> bit of performance data to back up that it's useful to add this code, >>> though. Have you run anything on eg kyber on nvme that shows a >>> reduction in overhead when getting rid of separate scheduler tags? >> >> I can observe small improvement in the following tests: >> >> 1) fio script >> # io scheduler: kyber >> >> RWS="randread read randwrite write" >> for RW in $RWS; do >> echo "Running test $RW" >> sudo echo 3 > /proc/sys/vm/drop_caches >> sudo fio --direct=1 --size=128G --bsrange=4k-4k --runtime=20 --numjobs=1 --ioengine=libaio --iodepth=10240 --group_reporting=1 --filename=$DISK --name=$DISK-test-$RW --rw=$RW --output-format=json >> done >> >> 2) results >> >> --------------------------------------------------------- >> |sched tag(iops/lat) | use hw tag to sched(iops/lat) >> ---------------------------------------------------------- >> randread |188940/54107 | 193865/52734 >> ---------------------------------------------------------- >> read |192646/53069 | 199738/51188 >> ---------------------------------------------------------- >> randwrite |171048/59777 | 179038/57112 >> ---------------------------------------------------------- >> write |171886/59492 | 181029/56491 >> ---------------------------------------------------------- >> >> I guess it may be a bit more obvious when running the test on one slow >> NVMe device, and will try to find one and run the test again. > > Thanks for running that. As I said in my original reply, I think this > is a good optimization, and the implementation is clean. I'm fine with > the current limitations of when to enable it, and it's not like we > can't extend this later, if we want. > > I do agree with Bart that patch 1+4 should be combined. I'll do that. Actually, can you do that when reposting? Looks like you needed to do that anyway. -- Jens Axboe
