On 06/25/2014 06:51 PM, Christoph Hellwig wrote:
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 nessecary decrement it after finishing all checks.Signed-off-by: Christoph Hellwig <h...@lst.de> --- drivers/scsi/scsi_lib.c | 52 ++++++++++++++++++++++++++------------------ include/scsi/scsi_device.h | 4 ++-- 2 files changed, 33 insertions(+), 23 deletions(-) diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c index 18e6449..5e269d6 100644 --- a/drivers/scsi/scsi_lib.c +++ b/drivers/scsi/scsi_lib.c @@ -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); } @@ -1305,37 +1305,49 @@ 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 (busy == 0 && starget->target_blocked) { /* * 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; + if (starget->target_blocked) + 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; } /* @@ -1445,7 +1457,7 @@ 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); @@ -1615,9 +1627,7 @@ 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 diff --git a/include/scsi/scsi_device.h b/include/scsi/scsi_device.h index 816e8a2..446f741 100644 --- a/include/scsi/scsi_device.h +++ b/include/scsi/scsi_device.h @@ -290,8 +290,8 @@ 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.
Reviewed-by: Hannes Reinecke <h...@suse.de> Cheers, Hannes -- Dr. Hannes Reinecke zSeries & Storage h...@suse.de +49 911 74053 688 SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg) -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
