From 328728630d9f2bf14b82ca30b5e47489beefe361 Mon Sep 17 00:00:00 2001 From: Ming Lei Date: Sun, 24 Jun 2018 22:03:27 +0800 Subject: scsi: core: avoid host-wide host_busy counter for scsi_mq It isn't necessary to check the host depth in scsi_queue_rq() any more since it has been respected by blk-mq before calling scsi_queue_rq() via getting driver tag. Lots of LUNs may attach to same host and per-host IOPS may reach millions, so we should avoid expensive atomic operations on the host-wide counter in the IO path. This patch implements scsi_host_busy() via blk_mq_tagset_busy_iter() for reading the count of busy IOs for scsi_mq. It is observed that IOPS is increased by 15% in IO test on scsi_debug (32 LUNs, 32 submit queues, 1024 can_queue, libaio/dio) in a dual-socket system. [mkp: clarified commit message] Cc: Omar Sandoval , Cc: "Martin K. Petersen" , Cc: James Bottomley , Cc: Christoph Hellwig , Cc: Don Brace Cc: Kashyap Desai Cc: Mike Snitzer Cc: Hannes Reinecke Cc: Laurence Oberman Cc: Bart Van Assche Signed-off-by: Ming Lei Reviewed-by: Bart Van Assche Signed-off-by: Martin K. Petersen --- drivers/scsi/hosts.c | 24 +++++++++++++++++++++++- drivers/scsi/scsi_lib.c | 23 +++++++++++++++++------ 2 files changed, 40 insertions(+), 7 deletions(-) diff --git a/drivers/scsi/hosts.c b/drivers/scsi/hosts.c index ea4b0bb0c1cd..f02dcc875a09 100644 --- a/drivers/scsi/hosts.c +++ b/drivers/scsi/hosts.c @@ -563,13 +563,35 @@ struct Scsi_Host *scsi_host_get(struct Scsi_Host *shost) } EXPORT_SYMBOL(scsi_host_get); +struct scsi_host_mq_in_flight { + int cnt; +}; + +static void scsi_host_check_in_flight(struct request *rq, void *data, + bool reserved) +{ + struct scsi_host_mq_in_flight *in_flight = data; + + if (blk_mq_request_started(rq)) + in_flight->cnt++; +} + /** * scsi_host_busy - Return the host busy counter * @shost: Pointer to Scsi_Host to inc. **/ int scsi_host_busy(struct Scsi_Host *shost) { - return atomic_read(&shost->host_busy); + struct scsi_host_mq_in_flight in_flight = { + .cnt = 0, + }; + + if (!shost->use_blk_mq) + return atomic_read(&shost->host_busy); + + blk_mq_tagset_busy_iter(&shost->tag_set, scsi_host_check_in_flight, + &in_flight); + return in_flight.cnt; } EXPORT_SYMBOL(scsi_host_busy); diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c index a1a0a2903263..600c78065d62 100644 --- a/drivers/scsi/scsi_lib.c +++ b/drivers/scsi/scsi_lib.c @@ -345,7 +345,8 @@ static void scsi_dec_host_busy(struct Scsi_Host *shost) unsigned long flags; rcu_read_lock(); - atomic_dec(&shost->host_busy); + if (!shost->use_blk_mq) + atomic_dec(&shost->host_busy); if (unlikely(scsi_host_in_recovery(shost))) { spin_lock_irqsave(shost->host_lock, flags); if (shost->host_failed || shost->host_eh_scheduled) @@ -444,7 +445,12 @@ static inline bool scsi_target_is_busy(struct scsi_target *starget) static inline bool scsi_host_is_busy(struct Scsi_Host *shost) { - if (shost->can_queue > 0 && + /* + * blk-mq can handle host queue busy efficiently via host-wide driver + * tag allocation + */ + + if (!shost->use_blk_mq && shost->can_queue > 0 && atomic_read(&shost->host_busy) >= shost->can_queue) return true; if (atomic_read(&shost->host_blocked) > 0) @@ -1600,9 +1606,12 @@ static inline int scsi_host_queue_ready(struct request_queue *q, if (scsi_host_in_recovery(shost)) return 0; - busy = atomic_inc_return(&shost->host_busy) - 1; + if (!shost->use_blk_mq) + busy = atomic_inc_return(&shost->host_busy) - 1; + else + busy = 0; if (atomic_read(&shost->host_blocked) > 0) { - if (busy) + if (busy || scsi_host_busy(shost)) goto starved; /* @@ -1616,7 +1625,7 @@ static inline int scsi_host_queue_ready(struct request_queue *q, "unblocking host at zero depth\n")); } - if (shost->can_queue > 0 && busy >= shost->can_queue) + if (!shost->use_blk_mq && shost->can_queue > 0 && busy >= shost->can_queue) goto starved; if (shost->host_self_blocked) goto starved; @@ -1702,7 +1711,9 @@ static void scsi_kill_request(struct request *req, struct request_queue *q) * with the locks as normal issue path does. */ atomic_inc(&sdev->device_busy); - atomic_inc(&shost->host_busy); + + if (!shost->use_blk_mq) + atomic_inc(&shost->host_busy); if (starget->can_queue > 0) atomic_inc(&starget->target_busy); -- cgit v1.2.3