Re: [PATCH] delay transition requeues for 2 seconds - alua

[Hannes Reinecke <hare@suse.de>]

On 01/03/2012 08:20 PM, Rob Evers wrote:
> From: Rob Evers <revers@redhat.com>
> 
> When alua targets are transitioning, the scsi midlayer retry mechanism
> continuously retries the scsi commands that are returning with not ready
> transitioning status.  The target is not capable of handling the
> commands for time on the order of several seconds during these transistions.
> 
> This patch delays the device queue for 2 seconds, which is in the same
> order of aas transition time.
> 
> Also, handle all other cases where ADD_TO_MLQUEUE_DELAY could be returned
> instead of ADD_TO_MLQUEUE as if ADD_TO_MLQUEUE were being returned.
> 
> Problem found by array partner testing
> 
> change MLQUEUE_DEV_DLY_RTY to MLQUEUE_DELAYED_RETRY
> 
I have been working on a different solution, whic
> Signed-off-by: Rob Evers <revers@redhat.com>
> ---
>  drivers/scsi/device_handler/scsi_dh_alua.c |    7 ++++---
>  drivers/scsi/scsi.c                        |    3 +++
>  drivers/scsi/scsi_error.c                  |    1 +
>  drivers/scsi/scsi_lib.c                    |    9 ++++++++-
>  include/scsi/scsi.h                        |   12 +++++++-----
>  5 files changed, 23 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/scsi/device_handler/scsi_dh_alua.c b/drivers/scsi/device_handler/scsi_dh_alua.c
> index 4ef0212..33b8df7 100644
> --- a/drivers/scsi/device_handler/scsi_dh_alua.c
> +++ b/drivers/scsi/device_handler/scsi_dh_alua.c
> @@ -233,7 +233,7 @@ static void stpg_endio(struct request *req, int error)
>  			goto done;
>  		}
>  		err = alua_check_sense(h->sdev, &sense_hdr);
> -		if (err == ADD_TO_MLQUEUE) {
> +		if (err == ADD_TO_MLQUEUE || err == ADD_TO_MLQUEUE_DELAY) {
>  			err = SCSI_DH_RETRY;
>  			goto done;
>  		}
> @@ -443,7 +443,7 @@ static int alua_check_sense(struct scsi_device *sdev,
>  			/*
>  			 * LUN Not Accessible - ALUA state transition
>  			 */
> -			return ADD_TO_MLQUEUE;
> +			return ADD_TO_MLQUEUE_DELAY;
>  		if (sense_hdr->asc == 0x04 && sense_hdr->ascq == 0x0b)
>  			/*
>  			 * LUN Not Accessible -- Target port in standby state
> @@ -521,7 +521,8 @@ static int alua_rtpg(struct scsi_device *sdev, struct alua_dh_data *h)
>  			return SCSI_DH_IO;
>  
>  		err = alua_check_sense(sdev, &sense_hdr);
> -		if (err == ADD_TO_MLQUEUE && time_before(jiffies, expiry))
> +		if ((err == ADD_TO_MLQUEUE || err == ADD_TO_MLQUEUE_DELAY) &&
> +		    time_before(jiffies, expiry))
>  			goto retry;
>  		sdev_printk(KERN_INFO, sdev,
>  			    "%s: rtpg sense code %02x/%02x/%02x\n",
Actually, this doesn't help if the RTPG command returns with the
mentioned error; then you'll just continue flooding the array with
RTPG commands. You'll need to delay the RTPG commands, too.

I'll be sending an updated patch.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
hare@suse.de			      +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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