scsi: remove performance regression due to async queue run

Commit c21e6beb removed our queue request_fn re-enter
protection, and defaulted to always running the queues from
kblockd to be safe. This was a known potential slow down,
but should be safe.

Unfortunately this is causing big performance regressions for
some, so we need to improve this logic. Looking into the details
of the re-enter, the real issue is on requeue of requests.

Requeue of requests upon seeing a BUSY condition from the device
ends up re-running the queue, causing traces like this:

scsi_request_fn()
        scsi_dispatch_cmd()
                scsi_queue_insert()
                        __scsi_queue_insert()
                                scsi_run_queue()
					scsi_request_fn()
						...

potentially causing the issue we want to avoid. So special
case the requeue re-run of the queue, but improve it to offload
the entire run of local queue and starved queue from a single
workqueue callback. This is a lot better than potentially
kicking off a workqueue run for each device seen.

This also fixes the issue of the local device going into recursion,
since the above mentioned commit never moved that queue run out
of line.

Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index e9901b8f8443ec3cf6b75487cf36d57584bccd17..01e4e51c4b68e262f3bbcde4474648d91555e990 100644 (file)
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -74,8 +74,6 @@ struct kmem_cache *scsi_sdb_cache;
  */
 #define SCSI_QUEUE_DELAY       3
 
-static void scsi_run_queue(struct request_queue *q);
-
 /*
  * Function:   scsi_unprep_request()
  *
@@ -161,7 +159,7 @@ static int __scsi_queue_insert(struct scsi_cmnd *cmd, int reason, int unbusy)
        blk_requeue_request(q, cmd->request);
        spin_unlock_irqrestore(q->queue_lock, flags);
 
-       scsi_run_queue(q);
+       kblockd_schedule_work(q, &device->requeue_work);
 
        return 0;
 }
@@ -433,7 +431,11 @@ static void scsi_run_queue(struct request_queue *q)
                        continue;
                }
 
-               blk_run_queue_async(sdev->request_queue);
+               spin_unlock(shost->host_lock);
+               spin_lock(sdev->request_queue->queue_lock);
+               __blk_run_queue(sdev->request_queue);
+               spin_unlock(sdev->request_queue->queue_lock);
+               spin_lock(shost->host_lock);
        }
        /* put any unprocessed entries back */
        list_splice(&starved_list, &shost->starved_list);
@@ -442,6 +444,16 @@ static void scsi_run_queue(struct request_queue *q)
        blk_run_queue(q);
 }
 
+void scsi_requeue_run_queue(struct work_struct *work)
+{
+       struct scsi_device *sdev;
+       struct request_queue *q;
+
+       sdev = container_of(work, struct scsi_device, requeue_work);
+       q = sdev->request_queue;
+       scsi_run_queue(q);
+}
+
 /*
  * Function:   scsi_requeue_command()
  *

diff --git a/drivers/scsi/scsi_scan.c b/drivers/scsi/scsi_scan.c
index 087821fac8fe76d64b50b0beaad7b1dd3c2dff0c..58584dc0724ade4fb4b2d5fc12d48b962d2b91bd 100644 (file)
--- a/drivers/scsi/scsi_scan.c
+++ b/drivers/scsi/scsi_scan.c
@@ -242,6 +242,7 @@ static struct scsi_device *scsi_alloc_sdev(struct scsi_target *starget,
        int display_failure_msg = 1, ret;
        struct Scsi_Host *shost = dev_to_shost(starget->dev.parent);
        extern void scsi_evt_thread(struct work_struct *work);
+       extern void scsi_requeue_run_queue(struct work_struct *work);
 
        sdev = kzalloc(sizeof(*sdev) + shost->transportt->device_size,
                       GFP_ATOMIC);
@@ -264,6 +265,7 @@ static struct scsi_device *scsi_alloc_sdev(struct scsi_target *starget,
        INIT_LIST_HEAD(&sdev->event_list);
        spin_lock_init(&sdev->list_lock);
        INIT_WORK(&sdev->event_work, scsi_evt_thread);
+       INIT_WORK(&sdev->requeue_work, scsi_requeue_run_queue);
 
        sdev->sdev_gendev.parent = get_device(&starget->dev);
        sdev->sdev_target = starget;

diff --git a/include/scsi/scsi_device.h b/include/scsi/scsi_device.h
index 2d3ec509468557521a65ac7fb016eff3728dcd59..dd82e02ddde3d353d657b6fd8e7e08feff7fa0ad 100644 (file)
--- a/include/scsi/scsi_device.h
+++ b/include/scsi/scsi_device.h
@@ -169,6 +169,7 @@ struct scsi_device {
                                sdev_dev;
 
        struct execute_work     ew; /* used to get process context on put */
+       struct work_struct      requeue_work;
 
        struct scsi_dh_data     *scsi_dh_data;
        enum scsi_device_state sdev_state;