Re: Perfromance drop on SCSI hard disk

["Alex,Shi" <alex.shi@intel.com>]

On Thu, 2011-05-19 at 16:26 +0800, Alex,Shi wrote:
> > 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? 

BTW, Jens, this patch is against on latest kernel, 2.6.39. 
> 
> 
> 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;
>