> > > I also noticed nr_hw_queues are now exposed in sysfs - > > > > > > > /sys/devices/pci0000:85/0000:85:00.0/0000:86:00.0/0000:87:04.0/0000:8b > > > > > > :00.0/0000:8c:00.0/0000:8d:00.0/host14/scsi_host/host14/nr_hw_queues:1 > > > 28 > > > . > > > > That's on my v8 wip branch, so I guess you're picking it up from there. > > John - I did more testing on v8 wip branch. CPU hotplug is working as > expected, but I still see some performance issue on Logical Volumes. > > I created 8 Drives Raid-0 VD on MR controller and below is performance > impact of this RFC. Looks like contention is on single <sdev>. > > I used command - "numactl -N 1 fio 1vd.fio --iodepth=128 --bs=4k -- > rw=randread --cpus_allowed_policy=split --ioscheduler=none -- > group_reporting --runtime=200 --numjobs=1" > IOPS without RFC = 300K IOPS with RFC = 230K. > > Perf top (shared host tag. IOPS = 230K) > > 13.98% [kernel] [k] sbitmap_any_bit_set > 6.43% [kernel] [k] blk_mq_run_hw_queue blk_mq_run_hw_queue function take more CPU which is called from " scsi_end_request" It looks like " blk_mq_hctx_has_pending" handles only elevator (scheduler) case. If queue has ioscheduler=none, we can skip. I case of scheduler=none, IO will be pushed to hardware queue and it by pass software queue. Based on above understanding, I added below patch and I can see performance scale back to expectation. Ming mentioned that - we cannot remove blk_mq_run_hw_queues() from IO completion path otherwise we may see IO hang. So I have just modified completion path assuming it is only required for IO scheduler case. https://www.spinics.net/lists/linux-block/msg55049.html Please review and let me know if this is good or we have to address with proper fix. diff --git a/block/blk-mq.c b/block/blk-mq.c index 1be7ac5a4040..b6a5b41b7fc2 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -1559,6 +1559,9 @@ void blk_mq_run_hw_queues(struct request_queue *q, bool async) struct blk_mq_hw_ctx *hctx; int i; + if (!q->elevator) + return; + queue_for_each_hw_ctx(q, hctx, i) { if (blk_mq_hctx_stopped(hctx)) continue; Kashyap > 6.00% [kernel] [k] __audit_syscall_exit > 3.47% [kernel] [k] read_tsc > 3.19% [megaraid_sas] [k] complete_cmd_fusion > 3.19% [kernel] [k] irq_entries_start > 2.75% [kernel] [k] blk_mq_run_hw_queues > 2.45% fio [.] fio_gettime > 1.76% [kernel] [k] entry_SYSCALL_64 > 1.66% [kernel] [k] add_interrupt_randomness > 1.48% [megaraid_sas] [k] megasas_build_and_issue_cmd_fusion > 1.42% [kernel] [k] copy_user_generic_string > 1.36% [kernel] [k] scsi_queue_rq > 1.03% [kernel] [k] kmem_cache_alloc > 1.03% [kernel] [k] internal_get_user_pages_fast > 1.01% [kernel] [k] swapgs_restore_regs_and_return_to_usermode > 0.96% [kernel] [k] kmem_cache_free > 0.88% [kernel] [k] blkdev_direct_IO > 0.84% fio [.] td_io_queue > 0.83% [kernel] [k] __get_user_4 > > Perf top (shared host tag. IOPS = 300K) > > 6.36% [kernel] [k] unroll_tree_refs > 5.77% [kernel] [k] __do_softirq > 4.56% [kernel] [k] irq_entries_start > 4.38% [kernel] [k] read_tsc > 3.95% [megaraid_sas] [k] complete_cmd_fusion > 3.21% fio [.] fio_gettime > 2.98% [kernel] [k] add_interrupt_randomness > 1.79% [kernel] [k] entry_SYSCALL_64 > 1.61% [kernel] [k] copy_user_generic_string > 1.61% [megaraid_sas] [k] megasas_build_and_issue_cmd_fusion > 1.34% [kernel] [k] scsi_queue_rq > 1.11% [kernel] [k] kmem_cache_free > 1.05% [kernel] [k] blkdev_direct_IO > 1.05% [kernel] [k] internal_get_user_pages_fast > 1.00% [kernel] [k] __memset > 1.00% fio [.] td_io_queue > 0.98% [kernel] [k] kmem_cache_alloc > 0.94% [kernel] [k] __get_user_4 > 0.93% [kernel] [k] lookup_ioctx > 0.88% [kernel] [k] sbitmap_any_bit_set > > Kashyap > > > > > Thanks, > > John
