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authorChristoph Hellwig <hch@lst.de>2014-06-25 20:05:56 -0600
committerJens Axboe <axboe@fb.com>2015-04-02 12:12:27 -0600
commit1286640eddf5b5d2c8c9f142e022b78528377138 (patch)
tree337e1f5765348de6ffd6f5985a5abc0a4d2a6828
parent15432819f26a66ae394ac86a9336cd52f8c878b7 (diff)
scsi: push host_lock down into scsi_{host,target}_queue_ready
Prepare for not taking a host-wide lock in the dispatch path by pushing the lock down into the places that actually need it. Note that this patch is just a preparation step, as it will actually increase lock roundtrips and thus decrease performance on its own. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Jens Axboe <axboe@fb.com>
-rw-r--r--drivers/scsi/scsi_lib.c74
1 files changed, 39 insertions, 35 deletions
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index be8ba66311de..2a7b0f00a79c 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -1296,18 +1296,18 @@ static inline int scsi_dev_queue_ready(struct request_queue *q,
/*
* scsi_target_queue_ready: checks if there we can send commands to target
* @sdev: scsi device on starget to check.
- *
- * Called with the host lock held.
*/
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;
+ spin_lock_irq(shost->host_lock);
if (starget->single_lun) {
if (starget->starget_sdev_user &&
starget->starget_sdev_user != sdev)
- return 0;
+ goto out;
starget->starget_sdev_user = sdev;
}
@@ -1315,19 +1315,23 @@ static inline int scsi_target_queue_ready(struct Scsi_Host *shost,
/*
* unblock after target_blocked iterates to zero
*/
- if (--starget->target_blocked == 0) {
- SCSI_LOG_MLQUEUE(3, starget_printk(KERN_INFO, starget,
- "unblocking target at zero depth\n"));
- } else
- return 0;
+ if (--starget->target_blocked != 0)
+ goto out;
+
+ 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);
- return 0;
+ goto out;
}
- return 1;
+ scsi_target(sdev)->target_busy++;
+ ret = 1;
+out:
+ spin_unlock_irq(shost->host_lock);
+ return ret;
}
/*
@@ -1335,37 +1339,43 @@ static inline int scsi_target_queue_ready(struct Scsi_Host *shost,
* return 0. We must end up running the queue again whenever 0 is
* returned, else IO can hang.
*
- * Called with host_lock held.
*/
static inline int scsi_host_queue_ready(struct request_queue *q,
struct Scsi_Host *shost,
struct scsi_device *sdev)
{
+ int ret = 0;
+
+ spin_lock_irq(shost->host_lock);
+
if (scsi_host_in_recovery(shost))
- return 0;
+ goto out;
if (shost->host_busy == 0 && shost->host_blocked) {
/*
* unblock after host_blocked iterates to zero
*/
- if (--shost->host_blocked == 0) {
- SCSI_LOG_MLQUEUE(3,
- printk("scsi%d unblocking host at zero depth\n",
- shost->host_no));
- } else {
- return 0;
- }
+ if (--shost->host_blocked != 0)
+ goto out;
+
+ SCSI_LOG_MLQUEUE(3,
+ shost_printk(KERN_INFO, shost,
+ "unblocking host at zero depth\n"));
}
if (scsi_host_is_busy(shost)) {
if (list_empty(&sdev->starved_entry))
list_add_tail(&sdev->starved_entry, &shost->starved_list);
- return 0;
+ goto out;
}
/* We're OK to process the command, so we can't be starved */
if (!list_empty(&sdev->starved_entry))
list_del_init(&sdev->starved_entry);
- return 1;
+ shost->host_busy++;
+ ret = 1;
+out:
+ spin_unlock_irq(shost->host_lock);
+ return ret;
}
/*
@@ -1546,7 +1556,7 @@ static void scsi_request_fn(struct request_queue *q)
blk_start_request(req);
sdev->device_busy++;
- spin_unlock(q->queue_lock);
+ spin_unlock_irq(q->queue_lock);
cmd = req->special;
if (unlikely(cmd == NULL)) {
printk(KERN_CRIT "impossible request in %s.\n"
@@ -1556,7 +1566,6 @@ static void scsi_request_fn(struct request_queue *q)
blk_dump_rq_flags(req, "foo");
BUG();
}
- spin_lock(shost->host_lock);
/*
* We hit this when the driver is using a host wide
@@ -1567,9 +1576,11 @@ static void scsi_request_fn(struct request_queue *q)
* a run when a tag is freed.
*/
if (blk_queue_tagged(q) && !blk_rq_tagged(req)) {
+ spin_lock_irq(shost->host_lock);
if (list_empty(&sdev->starved_entry))
list_add_tail(&sdev->starved_entry,
&shost->starved_list);
+ spin_unlock_irq(shost->host_lock);
goto not_ready;
}
@@ -1577,16 +1588,7 @@ static void scsi_request_fn(struct request_queue *q)
goto not_ready;
if (!scsi_host_queue_ready(q, shost, sdev))
- goto not_ready;
-
- scsi_target(sdev)->target_busy++;
- shost->host_busy++;
-
- /*
- * XXX(hch): This is rather suboptimal, scsi_dispatch_cmd will
- * take the lock again.
- */
- spin_unlock_irq(shost->host_lock);
+ goto host_not_ready;
/*
* Finally, initialize any error handling parameters, and set up
@@ -1609,9 +1611,11 @@ static void scsi_request_fn(struct request_queue *q)
return;
- not_ready:
+ host_not_ready:
+ spin_lock_irq(shost->host_lock);
+ scsi_target(sdev)->target_busy--;
spin_unlock_irq(shost->host_lock);
-
+ not_ready:
/*
* lock q, handle tag, requeue req, and decrement device_busy. We
* must return with queue_lock held.