[SCSI] qla2xxx: Conditionally disable automatic queue full tracking.

Changing a lun's queue depth (/sys/block/sdX/device/queue_depth)
isn't sticky when the device is connected via a QLogic fibre
channel adapter.

The QLogic qla2xxx fibre channel driver dynamically adjusts a
lun's queue depth.  If a user has a specific need to limit the
number of commands issued to a lun (say a tape drive, or a shared
raid where the total commands issued to all luns is limited at
the controller level, for example) and writes a limiting value to
/sys/block/sdXX/device/queue_depth, the qla2xxx driver will
silently and gradually increase the queue depth back to the
driver limit of ql2xmaxqdepth.  While reducing this value (module
parameter) or increasing the interval between ramp ups
(ql2xqfullrampup) offers the potential for a work around it would
be better to have the option of just disabling the dynamic
adjustment of queue depth.

This patch implements an "off switch" as a module parameter.

Signed-off-by: Michael Reed <mdr@sgi.com>
Signed-off-by: Andrew Vasquez <andrew.vasquez@qlogic.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>

1 files changed, 8 insertions, 0 deletions

diff --git a/drivers/scsi/qla2xxx/qla_os.c b/drivers/scsi/qla2xxx/qla_os.c
index 94e53a5fd9aa..155a204ed8e5 100644
--- a/drivers/scsi/qla2xxx/qla_os.c
+++ b/drivers/scsi/qla2xxx/qla_os.c
@@ -77,6 +77,14 @@ module_param(ql2xmaxqdepth, int, S_IRUGO|S_IWUSR);
 MODULE_PARM_DESC(ql2xmaxqdepth,
 		"Maximum queue depth to report for target devices.");
 
+int ql2xqfulltracking = 1;
+module_param(ql2xqfulltracking, int, S_IRUGO|S_IWUSR);
+MODULE_PARM_DESC(ql2xqfulltracking,
+		"Controls whether the driver tracks queue full status "
+		"returns and dynamically adjusts a scsi device's queue "
+		"depth.  Default is 1, perform tracking.  Set to 0 to "
+		"disable dynamic tracking and adjustment of queue depth.");
+
 int ql2xqfullrampup = 120;
 module_param(ql2xqfullrampup, int, S_IRUGO|S_IWUSR);
 MODULE_PARM_DESC(ql2xqfullrampup,