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. Applies to 2.6.28-rc6-git1.

Signed-off-by Michael Reed <[email protected]>

--- a/drivers/scsi/qla2xxx/qla_gbl.h 2008-11-11 08:57:26.000000000
-0600
+++ b/drivers/scsi/qla2xxx/qla_gbl.h 2008-11-24 10:11:48.948835394
-0600

drivers/scsi/qla2xxx/qla_gbl.h +21 -6

@@ -62,6 +62,7 @@ extern int ql2xfdmienable;
 extern int ql2xallocfwdump;
 extern int ql2xextended_error_logging;
 extern int ql2xqfullrampup;
+extern int ql2xqfulltracking;
 extern int ql2xiidmaenable;
 
 extern int qla2x00_loop_reset(scsi_qla_host_t *);
--- a/drivers/scsi/qla2xxx/qla_isr.c	2008-11-11 08:57:26.000000000  
-0600
+++ b/drivers/scsi/qla2xxx/qla_isr.c	2008-11-21 17:23:46.065443427  
-0600

@@ -691,6 +691,9 @@ qla2x00_adjust_sdev_qdepth_up(struct scs
 {
 	fc_port_t *fcport = data;
 
+	if (!ql2xqfulltracking)
+		return;
+
 	if (fcport->ha->max_q_depth <= sdev->queue_depth)
 		return;
 

@@ -729,6 +732,9 @@ qla2x00_ramp_up_queue_depth(scsi_qla_hos
 	fc_port_t *fcport;
 	struct scsi_device *sdev;
 
+	if (!ql2xqfulltracking)
+		return;
+
 	sdev = sp->cmd->device;
 	if (sdev->queue_depth >= ha->max_q_depth)
 		return;

@@ -1043,6 +1049,8 @@ qla2x00_status_entry(scsi_qla_host_t *ha
 			    scsi_status));
 
 			/* Adjust queue depth for all luns on the port. */
+			if (!ql2xqfulltracking)
+				break;
 			fcport->last_queue_full = jiffies;
 			starget_for_each_device(cp->device->sdev_target,
 			    fcport, qla2x00_adjust_sdev_qdepth_down);

@@ -1102,6 +1110,8 @@ qla2x00_status_entry(scsi_qla_host_t *ha
 				 * Adjust queue depth for all luns on the
 				 * port.
 				 */
+				if (!ql2xqfulltracking)
+					break;
 				fcport->last_queue_full = jiffies;
 				starget_for_each_device(
 				    cp->device->sdev_target, fcport,
--- a/drivers/scsi/qla2xxx/qla_os.c	2008-11-11 08:57:26.000000000  
-0600
+++ b/drivers/scsi/qla2xxx/qla_os.c	2008-11-21 17:23:46.093443556  
-0600

@@ -79,6 +79,14 @@ module_param(ql2xmaxqdepth, int, S_IRUGO
 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,