From: Ming Lei ming.lei@redhat.com
mainline inclusion from mainline-v5.10-rc1 commit ed5dd6a67d5eac5fb8873697b55dc1699752a9f3 category: bugfix bugzilla: 47875 CVE: NA
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The request queue is currently run unconditionally in scsi_end_request() if both target queue and host queue are ready.
Recently Long Li reported that cost of a queue run can be very heavy in case of high queue depth. Improve this situation by only running the request queue when this LUN is busy.
Link: https://lore.kernel.org/r/20200910075056.36509-1-ming.lei@redhat.com Reported-by: Long Li longli@microsoft.com Tested-by: Long Li longli@microsoft.com Tested-by: Kashyap Desai kashyap.desai@broadcom.com Reviewed-by: Bart Van Assche bvanassche@acm.org Reviewed-by: Hannes Reinecke hare@suse.de Reviewed-by: Ewan D. Milne emilne@redhat.com Reviewed-by: John Garry john.garry@huawei.com Signed-off-by: Ming Lei ming.lei@redhat.com Signed-off-by: Martin K. Petersen martin.petersen@oracle.com Conflict: drivers/scsi/scsi_lib.c include/scsi/scsi_device.h Signed-off-by: Yufen Yu yuyufen@huawei.com Reviewed-by: Jason Yan yanaijie@huawei.com Signed-off-by: Yang Yingliang yangyingliang@huawei.com Signed-off-by: Cheng Jian cj.chengjian@huawei.com --- drivers/scsi/scsi_lib.c | 34 +++++++++++++++++++++++++++++++++- include/scsi/scsi_device.h | 1 + 2 files changed, 34 insertions(+), 1 deletion(-)
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c index 0d5255482ca1..1bca98745b00 100644 --- a/drivers/scsi/scsi_lib.c +++ b/drivers/scsi/scsi_lib.c @@ -695,7 +695,23 @@ static void scsi_run_queue_async(struct scsi_device *sdev) if (!kblockd_schedule_work(&sdev->requeue_work)) percpu_ref_put(&q->q_usage_counter); } else { - blk_mq_run_hw_queues(q, true); + /* + * smp_mb() present in sbitmap_queue_clear() or implied in + * .end_io is for ordering writing .device_busy in + * scsi_device_unbusy() and reading sdev->restarts. + */ + int old = atomic_read(&sdev->restarts); + + /* + * ->restarts has to be kept as non-zero if new budget + * contention occurs. + * + * No need to run queue when either another re-run + * queue wins in updating ->restarts or a new budget + * contention occurs. + */ + if (old && atomic_cmpxchg(&sdev->restarts, old, 0) == old) + blk_mq_run_hw_queues(sdev->request_queue, true); percpu_ref_put(&q->q_usage_counter); } } @@ -2136,7 +2152,23 @@ static bool scsi_mq_get_budget(struct blk_mq_hw_ctx *hctx)
out_put_device: put_device(&sdev->sdev_gendev); + atomic_inc(&sdev->restarts); + + /* + * Orders atomic_inc(&sdev->restarts) and atomic_read(&sdev->device_busy). + * .restarts must be incremented before .device_busy is read because the + * code in scsi_run_queue_async() depends on the order of these operations. + */ + smp_mb__after_atomic(); out: + /* + * If all in-flight requests originated from this LUN are completed + * before reading .device_busy, sdev->device_busy will be observed as + * zero, then blk_mq_delay_run_hw_queues() will dispatch this request + * soon. Otherwise, completion of one of these requests will observe + * the .restarts flag, and the request queue will be run for handling + * this request, see scsi_end_request(). + */ if (atomic_read(&sdev->device_busy) == 0 && !scsi_device_blocked(sdev)) blk_mq_delay_run_hw_queue(hctx, SCSI_QUEUE_DELAY); return false; diff --git a/include/scsi/scsi_device.h b/include/scsi/scsi_device.h index 550739a5ea96..6e2edd66c598 100644 --- a/include/scsi/scsi_device.h +++ b/include/scsi/scsi_device.h @@ -110,6 +110,7 @@ struct scsi_device { atomic_t device_busy; /* commands actually active on LLDD */ atomic_t device_blocked; /* Device returned QUEUE_FULL. */
+ atomic_t restarts; spinlock_t list_lock; struct list_head cmd_list; /* queue of in use SCSI Command structures */ struct list_head starved_entry;