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 <hch@xxxxxx>
---
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 <hare@xxxxxxx>
Cheers,
Hannes
--
Dr. Hannes Reinecke zSeries & Storage
hare@xxxxxxx +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg)
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