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Commit 32872863 authored by Ming Lei's avatar Ming Lei Committed by Martin K. Petersen
Browse files

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 <osandov@fb.com>,
Cc: "Martin K. Petersen" <martin.petersen@oracle.com>,
Cc: James Bottomley <james.bottomley@hansenpartnership.com>,
Cc: Christoph Hellwig <hch@lst.de>,
Cc: Don Brace <don.brace@microsemi.com>
Cc: Kashyap Desai <kashyap.desai@broadcom.com>
Cc: Mike Snitzer <snitzer@redhat.com>
Cc: Hannes Reinecke <hare@suse.de>
Cc: Laurence Oberman <loberman@redhat.com>
Cc: Bart Van Assche <bart.vanassche@wdc.com>
Signed-off-by: default avatarMing Lei <ming.lei@redhat.com>
Reviewed-by: default avatarBart Van Assche <bart.vanassche@wdc.com>
Signed-off-by: default avatarMartin K. Petersen <martin.petersen@oracle.com>
parent c84b023a

drivers/scsi/hosts.c

+23 −1
Original line number Diff line number Diff line
@@ -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)

{

	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);

drivers/scsi/scsi_lib.c

+17 −6
Original line number Diff line number Diff line
@@ -345,6 +345,7 @@ static void scsi_dec_host_busy(struct Scsi_Host *shost) 
	unsigned long flags;



	rcu_read_lock();

	if (!shost->use_blk_mq)

		atomic_dec(&shost->host_busy);

	if (unlikely(scsi_host_in_recovery(shost))) {

		spin_lock_irqsave(shost->host_lock, flags);
@@ -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;



	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;
@@ -1702,6 +1711,8 @@ 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);



	if (!shost->use_blk_mq)

		atomic_inc(&shost->host_busy);

	if (starget->can_queue > 0)

		atomic_inc(&starget->target_busy);