blk-mq, elevator: Count requests per hctx to improve performance
High CPU utilization on "native_queued_spin_lock_slowpath" due to lock contention is possible for mq-deadline and bfq IO schedulers when nr_hw_queues is more than one. It is because kblockd work queue can submit IO from all online CPUs (through blk_mq_run_hw_queues()) even though only one hctx has pending commands. The elevator callback .has_work for mq-deadline and bfq scheduler considers pending work if there are any IOs on request queue but it does not account hctx context. Add a per-hctx 'elevator_queued' count to the hctx to avoid triggering the elevator even though there are no requests queued. [jpg: Relocated atomic_dec() in dd_dispatch_request(), update commit message per Kashyap] Signed-off-by:Kashyap Desai <kashyap.desai@broadcom.com> Signed-off-by:
Hannes Reinecke <hare@suse.de> Signed-off-by:
John Garry <john.garry@huawei.com> Tested-by:
Douglas Gilbert <dgilbert@interlog.com> Signed-off-by:
Jens Axboe <axboe@kernel.dk>
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