sym53c8xx uses a command queue depth of 2 for untagged devices, without good reason. This _mostly_ seems to work ok, but it has caused me some subtle problems. For example, I have an application where one thread sends write commands to a tape drive, and another thread sends log sense polling commands. With a queue depth of 2, the polling commands end up being starved for long periods of time while multiple write commands are serviced (this may also be related to the fact the the sg driver queues commands in LIFO order). This problem is fixed by changing the queue depth to 1 for untagged devices. I have tested this change extensively with many different tape drives, medium changers, and disk drives (disk drives of course use tagged commands and are therefore unaffected by this patch). Signed-off-by: Tony Battersby <tonyb@xxxxxxxxxxxxxxx> --- --- linux-2.6.28/drivers/scsi/sym53c8xx_2/sym_glue.c.orig 2009-01-08 10:53:39.000000000 -0500 +++ linux-2.6.28/drivers/scsi/sym53c8xx_2/sym_glue.c 2009-01-08 11:03:40.000000000 -0500 @@ -792,9 +792,9 @@ static int sym53c8xx_slave_configure(str /* * Select queue depth from driver setup. - * Donnot use more than configured by user. - * Use at least 2. - * Donnot use more than our maximum. + * Do not use more than configured by user. + * Use at least 1. + * Do not use more than our maximum. */ reqtags = sym_driver_setup.max_tag; if (reqtags > tp->usrtags) @@ -803,7 +803,7 @@ static int sym53c8xx_slave_configure(str reqtags = 0; if (reqtags > SYM_CONF_MAX_TAG) reqtags = SYM_CONF_MAX_TAG; - depth_to_use = reqtags ? reqtags : 2; + depth_to_use = reqtags ? reqtags : 1; scsi_adjust_queue_depth(sdev, sdev->tagged_supported ? MSG_SIMPLE_TAG : 0, depth_to_use); -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
