On Wed, Feb 03 2016 at 1:24pm -0500, Mike Snitzer <snitzer@xxxxxxxxxx> wrote: > > Here are pictures of 'perf report' for perf datat collected using > > 'perf record -ag -e cs'. > > > > Against null_blk: > > http://people.redhat.com/msnitzer/perf-report-cs-null_blk.png > > if dm-mq nr_hw_queues=1 and null_blk nr_hw_queues=1 > cpu : usr=25.53%, sys=74.40%, ctx=1970, majf=0, minf=474 > if dm-mq nr_hw_queues=1 and null_blk nr_hw_queues=4 > cpu : usr=26.79%, sys=73.15%, ctx=2067, majf=0, minf=479 > > > Against dm-mpath ontop of the same null_blk: > > http://people.redhat.com/msnitzer/perf-report-cs-dm_mq.png > > if dm-mq nr_hw_queues=1 and null_blk nr_hw_queues=1 > cpu : usr=11.07%, sys=33.90%, ctx=667784, majf=0, minf=466 > if dm-mq nr_hw_queues=1 and null_blk nr_hw_queues=4 > cpu : usr=15.22%, sys=48.44%, ctx=2314901, majf=0, minf=466 I promise, this is my last reply to myself ;) The above dm-mq results were _without_ using this commit: "dm: don't blk_mq_run_hw_queues in blk-mq request completion" https://git.kernel.org/cgit/linux/kernel/git/device-mapper/linux-dm.git/commit/?h=dm-4.6&id=cc6ca783e8f0669112c5f4154f51a7cb17b76006 But with that commit I'm still seeing the high context switches: if dm-mq nr_hw_queues=1 and null_blk nr_hw_queues=1 cpu : usr=11.78%, sys=36.11%, ctx=690262, majf=0, minf=470 if dm-mq nr_hw_queues=1 and null_blk nr_hw_queues=4 cpu : usr=15.62%, sys=49.95%, ctx=2425084, majf=0, minf=466 So running blk_mq_run_hw_queues (async to punt to kblockd) on dm-mq request completion isn't the source of any of the accounted context switches... -- To unsubscribe from this list: send the line "unsubscribe linux-block" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
