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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: Christoph Hellwig <hch@lst.de>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Webb Scales <webbnh@hp.com>
Acked-by: Jens Axboe <axboe@kernel.dk>
Tested-by: Bart Van Assche <bvanassche@acm.org>
Tested-by: Robert Elliott <elliott@hp.com>
This commit is contained in:
Christoph Hellwig 2014-01-22 14:49:41 +01:00
parent cf68d334dd
commit 7ae65c0f96
2 changed files with 34 additions and 23 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

53
drivers/scsi/scsi_lib.c
View File

@ -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

4
include/scsi/scsi_device.h
View File

@ -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.