Re: [PATCH] scsi/block: increase flush/sync timeout

[Boaz Harrosh <bharrosh@panasas.com>]

On 08/03/2010 10:26 PM, michaelc@cs.wisc.edu wrote:
> From: Mike Christie <mchristi@redhat.com>
> 
> We have been seeing the flush request timeout with a wide
> range of hardware from tgt+iser to FC targets from a major vendor.
> 
> I did this patch which added a flush timeout:
> http://marc.info/?l=linux-scsi&m=127957359200466&w=2
> 
> A problem with that patch is how to determine what value
> should be set and when you need to set it. You will
> not know that you need to increase until it times out
> and fails, then to figure out what to set it to you
> need to set the timeout and try it out a couple times.
> 
> So this patch just increases the flush/sync cache timeout
> to 2 minutes. In testing, it has taken at most around 60
> seconds to complete the operation, so I thought 120 would
> be safe and not add that long of delay if the device was
> really jammed and needed the scsi eh.
> 
> Signed-off-by: Mike Christie <michaelc@cs.wisc.edu>

I'm not sure either way, but you might also use the
request_queue's timeout which is settable from user-mode,
times a factor like "request_queue->timeout * 4"

A slow device might be slower on flush as well.

Or not, just an option ;-)
(Or be really smart like can_queue * single_io_timeout / 2)

Boaz

> ---
>  drivers/scsi/sd.c |    4 ++--
>  drivers/scsi/sd.h |    1 +
>  2 files changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
> index 108daea..3ef08bd 100644
> --- a/drivers/scsi/sd.c
> +++ b/drivers/scsi/sd.c
> @@ -477,7 +477,7 @@ static int scsi_setup_discard_cmnd(struct scsi_device *sdp, struct request *rq)
>  
>  static int scsi_setup_flush_cmnd(struct scsi_device *sdp, struct request *rq)
>  {
> -	rq->timeout = SD_TIMEOUT;
> +	rq->timeout = SD_FLUSH_TIMEOUT;
>  	rq->retries = SD_MAX_RETRIES;
>  	rq->cmd[0] = SYNCHRONIZE_CACHE;
>  	rq->cmd_len = 10;
> @@ -1064,7 +1064,7 @@ static int sd_sync_cache(struct scsi_disk *sdkp)
>  		 * flush everything.
>  		 */
>  		res = scsi_execute_req(sdp, cmd, DMA_NONE, NULL, 0, &sshdr,
> -				       SD_TIMEOUT, SD_MAX_RETRIES, NULL);
> +				       SD_FLUSH_TIMEOUT, SD_MAX_RETRIES, NULL);
>  		if (res == 0)
>  			break;
>  	}
> diff --git a/drivers/scsi/sd.h b/drivers/scsi/sd.h
> index f81a930..86e6dc3 100644
> --- a/drivers/scsi/sd.h
> +++ b/drivers/scsi/sd.h
> @@ -19,6 +19,7 @@
>   */
>  #define SD_TIMEOUT		(30 * HZ)
>  #define SD_MOD_TIMEOUT		(75 * HZ)
> +#define SD_FLUSH_TIMEOUT	(120 * HZ)
>  
>  /*
>   * Number of allowed retries