linux-kernel - [PATCH] drivers/scsi/qla1280.c; was Re: Buffered I/O to block device very slow and other SCSI issues...

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Date:	Sun, 11 May 2008 23:17:03 -0700
From:	Jeremy Higdon <jeremy@....com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	David Chinner <dgc@....com>, lkml <linux-kernel@...r.kernel.org>,
	linux-scsi@...r.kernel.org, Jens Axboe <jens.axboe@...cle.com>,
	jes@....com
Subject: [PATCH] drivers/scsi/qla1280.c; was Re: Buffered I/O to block device very slow and other SCSI issues...

On Thu, Mar 20, 2008 at 03:20:10AM -0700, Andrew Morton wrote:
> > > I also suspect that CTQ has not been set up correctly on this
> > > kernel, because:
> > > 
> > > $ cat /sys/block/sdb/device/queue_depth
> > > 3
> > > $ ls -l /sys/block/sdb/device/queue_depth
> > > -r--r--r-- 1 root root 0 Mar 20 09:59 /sys/block/sdb/device/queue_depth
> > > $
> > > 
> > > It appears to be hard coded to 3 and can't be changed....
> > 
> > That's a bug in the qla1280 driver.  I thought that had gotten fixed.
> > It's looking at the wrong mailbox register after setting device parameters.
> 
> Was there a patch anywhere?

Promised patch...

The qla1280 driver was ANDing the output value of mailbox register
0 with (1 << target-number) to determine whether to enable queueing
on the target in question.

But mailbox register 0 has the status code for the mailbox command
(in this case, Set Target Parameters).  Potential values are:
/*      
 * ISP mailbox command complete status codes
 */
#define MBS_CMD_CMP             0x4000  /* Command Complete. */
#define MBS_INV_CMD             0x4001  /* Invalid Command. */
#define MBS_HOST_INF_ERR        0x4002  /* Host Interface Error. */
#define MBS_TEST_FAILED         0x4003  /* Test Failed. */
#define MBS_CMD_ERR             0x4005  /* Command Error. */
#define MBS_CMD_PARAM_ERR       0x4006  /* Command Parameter Error. */

So clearly that is in error.  I can't think what the author of that
line was looking for in a mailbox register, so I just eliminated the
AND.  flag is used later in the function, and I think that the later
usage was also wrong, though it was used to set values that aren't
used.  Oh well, an overhaul of this driver is not what I want to do
now -- just a bugfix. 

After the fix, I found that my disks were getting a queue depth of
255, which is far too many.  Most SCSI disks are limited to 32 or
64.  In any case, there's no point, queueing up a bunch of commands
to the adapter that will just result in queue full or starve other
targets from being issued commands due to running out of internal
memory.  So I dropped default queue depth to 32 (from which 1 is
subtracted elsewhere, giving net of 31).

I tested with a Seagate ST336753LC, and results look good, so
I'm satisfied with this patch.

Signed-off-by: Jeremy Higdon <jeremy@....com>

---

--- a/drivers/scsi/qla1280.c	2008-05-03 11:59:44.000000000 -0700
+++ b/drivers/scsi/qla1280.c	2008-05-10 21:32:23.451341969 -0700
@@ -2007,7 +2007,7 @@ qla1280_set_defaults(struct scsi_qla_hos
 		nv->bus[bus].config_2.req_ack_active_negation = 1;
 		nv->bus[bus].config_2.data_line_active_negation = 1;
 		nv->bus[bus].selection_timeout = 250;
-		nv->bus[bus].max_queue_depth = 256;
+		nv->bus[bus].max_queue_depth = 32;

 		if (IS_ISP1040(ha)) {
 			nv->bus[bus].bus_reset_delay = 3;
@@ -2051,7 +2051,7 @@ qla1280_config_target(struct scsi_qla_ho
 	status = qla1280_mailbox_command(ha, 0x0f, mb);

 	/* Save Tag queuing enable flag. */
-	flag = (BIT_0 << target) & mb[0];
+	flag = (BIT_0 << target);
 	if (nv->bus[bus].target[target].parameter.tag_queuing)
 		ha->bus_settings[bus].qtag_enables |= flag;

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