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Commit 7ae65c0f authored by Christoph Hellwig's avatar Christoph Hellwig
Browse files

scsi: convert target_busy to an atomic_t 



Avoid taking the host-wide host_lock to check the per-target queue limit.
Instead we do an atomic_inc_return early on to grab our slot in the queue,
and if necessary decrement it after finishing all checks.

Signed-off-by: default avatarChristoph Hellwig <hch@lst.de>
Reviewed-by: default avatarMartin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: default avatarHannes Reinecke <hare@suse.de>
Reviewed-by: default avatarWebb Scales <webbnh@hp.com>
Acked-by: default avatarJens Axboe <axboe@kernel.dk>
Tested-by: default avatarBart Van Assche <bvanassche@acm.org>
Tested-by: default avatarRobert Elliott <elliott@hp.com>
parent cf68d334

drivers/scsi/scsi_lib.c

+32 −21
Original line number Diff line number Diff line
@@ -294,7 +294,7 @@ void scsi_device_unbusy(struct scsi_device *sdev) 


	spin_lock_irqsave(shost->host_lock, flags);

	shost->host_busy--;

	starget->target_busy--;

	atomic_dec(&starget->target_busy);

	if (unlikely(scsi_host_in_recovery(shost) &&

		     (shost->host_failed || shost->host_eh_scheduled)))

		scsi_eh_wakeup(shost);
@@ -361,7 +361,7 @@ static inline int scsi_device_is_busy(struct scsi_device *sdev) 
static inline int scsi_target_is_busy(struct scsi_target *starget)

{

	return ((starget->can_queue > 0 &&

		 starget->target_busy >= starget->can_queue) ||

		 atomic_read(&starget->target_busy) >= starget->can_queue) ||

		 starget->target_blocked);

}
@@ -1279,37 +1279,50 @@ static inline int scsi_target_queue_ready(struct Scsi_Host *shost, 
					   struct scsi_device *sdev)

{

	struct scsi_target *starget = scsi_target(sdev);

	int ret = 0;

	unsigned int busy;



	spin_lock_irq(shost->host_lock);

	if (starget->single_lun) {

		spin_lock_irq(shost->host_lock);

		if (starget->starget_sdev_user &&

		    starget->starget_sdev_user != sdev)

			goto out;

		    starget->starget_sdev_user != sdev) {

			spin_unlock_irq(shost->host_lock);

			return 0;

		}

		starget->starget_sdev_user = sdev;

		spin_unlock_irq(shost->host_lock);

	}



	if (starget->target_busy == 0 && starget->target_blocked) {

	busy = atomic_inc_return(&starget->target_busy) - 1;

	if (starget->target_blocked) {

		if (busy)

			goto starved;



		/*

		 * unblock after target_blocked iterates to zero

		 */

		if (--starget->target_blocked != 0)

			goto out;

		spin_lock_irq(shost->host_lock);

		if (--starget->target_blocked != 0) {

			spin_unlock_irq(shost->host_lock);

			goto out_dec;

		}

		spin_unlock_irq(shost->host_lock);



		SCSI_LOG_MLQUEUE(3, starget_printk(KERN_INFO, starget,

				 "unblocking target at zero depth\n"));

	}



	if (scsi_target_is_busy(starget)) {

		list_move_tail(&sdev->starved_entry, &shost->starved_list);

		goto out;

	}

	if (starget->can_queue > 0 && busy >= starget->can_queue)

		goto starved;



	scsi_target(sdev)->target_busy++;

	ret = 1;

out:

	return 1;



starved:

	spin_lock_irq(shost->host_lock);

	list_move_tail(&sdev->starved_entry, &shost->starved_list);

	spin_unlock_irq(shost->host_lock);

	return ret;

out_dec:

	atomic_dec(&starget->target_busy);

	return 0;

}



/*
@@ -1419,7 +1432,7 @@ static void scsi_kill_request(struct request *req, struct request_queue *q) 
	spin_unlock(sdev->request_queue->queue_lock);

	spin_lock(shost->host_lock);

	shost->host_busy++;

	starget->target_busy++;

	atomic_inc(&starget->target_busy);

	spin_unlock(shost->host_lock);

	spin_lock(sdev->request_queue->queue_lock);
@@ -1589,9 +1602,7 @@ static void scsi_request_fn(struct request_queue *q) 
	return;



 host_not_ready:

	spin_lock_irq(shost->host_lock);

	scsi_target(sdev)->target_busy--;

	spin_unlock_irq(shost->host_lock);

	atomic_dec(&scsi_target(sdev)->target_busy);

 not_ready:

	/*

	 * lock q, handle tag, requeue req, and decrement device_busy. We

include/scsi/scsi_device.h

+2 −2
Original line number Diff line number Diff line
@@ -291,8 +291,8 @@ struct scsi_target { 
	unsigned int		expecting_lun_change:1;	/* A device has reported

						 * a 3F/0E UA, other devices on

						 * the same target will also. */

	/* commands actually active on LLD. protected by host lock. */

	unsigned int		target_busy;

	/* commands actually active on LLD. */

	atomic_t		target_busy;

	/*

	 * LLDs should set this in the slave_alloc host template callout.

	 * If set to zero then there is not limit.