Alan Cox wrote:
> On Wed, 2003-03-12 at 23:06, Mark Haverkamp wrote:
>
>>During probe, scsi_alloc_sdev is called. It calls
>>scsi_adjust_queue_depth with the cmd_per_lun value.
>>scsi_adjust_queue_depth returns without doing anything if the tags value
>>is greater than 256. This leaves the Scsi_Device queue_depth at zero.
>>Later when an I/O is queued, scsi_request_fn checks for device_busy >=
>>queue_depth. If so, the function does a break and exits. This is where
>>it hangs.
>>
>>To get things to load I set cmd_per_lun to 256. I don't know if the is
>>the correct way to deal with the problem. Maybe someone else can say
>>something about that.
>
>
> If the SCSI layer is trying to be clever by ignoring the requested 512
> then thats the actual problem. 512 is the right value because its not
> really a disk you are talking to on the main channel. So the scsi layer
> ought to honour it.
Here is the relevant code snippet in scsi.c around line
930:
void scsi_adjust_queue_depth(Scsi_Device *SDpnt, int tagged, int tags)
{
static spinlock_t device_request_lock = SPIN_LOCK_UNLOCKED;
unsigned long flags;
/*
* refuse to set tagged depth to an unworkable size
*/
if(tags <= 0)
return;
/*
* Limit max queue depth on a single lun to 256 for now. Remember,
* we allocate a struct scsi_command for each of these and keep it
* around forever. Too deep of a depth just wastes memory.
*/
if(tags > 256)
return;
....
[pardon the wrap]
Now scsi_device::queue_depth is an unsigned short so that
is not a problem. Also the comment prior to the
"if (tags > 256)" is no longer correct (I think). So
perhaps it can be changed to "if (tags > 65535) ..."
Doug Gilbert
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This archive was generated by hypermail 2b29 : Sat Mar 15 2003 - 22:00:33 EST