In high-datarate aging tests, it is found that the
SCSI framework can periodically issue lu resets as
some commands timeout.
Response TASK SET FULL and SAS_QUEUE_FULL may be
returned many times for the same command, causing the
timeouts.
The SAS_QUEUE_FULL errors come from
TRANS_TX_CREDIT_TIMEOUT_ERR, TRANS_TX_CLOSE_NORMAL_ERR,
and TRANS_TX_ERR_FRAME_TXED errors. They do not mean
that the queue is full in the host, but rather it is
equivalent to meaning the queue is full for the sdev.
To overcome this, the queue depth for the sdev is
reduced to 64 (from 256, set in sas_slave_configure()).
Normally error code SAS_QUEUE_FULL will result in the
sdev queue depth falling, but it falls too slowly during
high-datarate tests and commands timeout before it
has fallen to an adequete level from original value.

Signed-off-by: John Garry <john.garry@huawei.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>