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SubjectRe: Perfromance drop on SCSI hard disk
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> I will queue up the combined patch, it looks fine from here as well.
>

When I have some time to study Jens and shaohua's patch today. I find a
simpler way to resolved the re-enter issue on starved_list. Following
Jens' idea, we can just put the starved_list device into kblockd if it
come from __scsi_queue_insert().
It can resolve the re-enter issue and recover performance totally, and
need not a work_struct in every scsi_device. The logic/code also looks a
bit simpler.
What's your opinion of this?


Signed-off-by: Alex Shi <alex.shi@intel.com>
---
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index ec1803a..de7c569 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -74,6 +74,8 @@ struct kmem_cache *scsi_sdb_cache;
*/
#define SCSI_QUEUE_DELAY 3

+static void scsi_run_queue_async(struct request_queue *q);
+
/*
* Function: scsi_unprep_request()
*
@@ -159,7 +161,7 @@ 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);

- kblockd_schedule_work(q, &device->requeue_work);
+ scsi_run_queue_async(q);

return 0;
}
@@ -395,7 +397,7 @@ static inline int scsi_host_is_busy(struct Scsi_Host *shost)
* Notes: The previous command was completely finished, start
* a new one if possible.
*/
-static void scsi_run_queue(struct request_queue *q)
+static void __scsi_run_queue(struct request_queue *q, bool async)
{
struct scsi_device *sdev = q->queuedata;
struct Scsi_Host *shost;
@@ -435,30 +437,35 @@ static void scsi_run_queue(struct request_queue *q)
&shost->starved_list);
continue;
}
-
- 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);
+ if (async)
+ blk_run_queue_async(sdev->request_queue);
+ else {
+ 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);
spin_unlock_irqrestore(shost->host_lock, flags);

- blk_run_queue(q);
+ if (async)
+ blk_run_queue_async(q);
+ else
+ blk_run_queue(q);
}

-void scsi_requeue_run_queue(struct work_struct *work)
+static void scsi_run_queue(struct request_queue *q)
{
- 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);
+ __scsi_run_queue(q, false);
}

+static void scsi_run_queue_async(struct request_queue *q)
+{
+ __scsi_run_queue(q, true);
+}
/*
* Function: scsi_requeue_command()
*
diff --git a/drivers/scsi/scsi_scan.c b/drivers/scsi/scsi_scan.c
index 58584dc..087821f 100644
--- a/drivers/scsi/scsi_scan.c
+++ b/drivers/scsi/scsi_scan.c
@@ -242,7 +242,6 @@ 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);
@@ -265,7 +264,6 @@ 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 dd82e02..2d3ec50 100644
--- a/include/scsi/scsi_device.h
+++ b/include/scsi/scsi_device.h
@@ -169,7 +169,6 @@ 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;



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