[PATCH] aic94xx: Increase can_queue and cmds_per_lun

["Darrick J. Wong" <djwong@us.ibm.com>]

Hi all,

Below is a patch that sets cmd_per_lun and can_queue in the aic94xx
driver's scsi_host_template to better performing values than what's
there currently.  The cmd_per_lun setting is stolen straight out of the
adp94xx source, and can_queue is derived from the max_scb value that we
calculate in asd_init_hw.  To the best of my (admittedly limited)
knowledge, this method provides the correct values (can_queue = 443 in
both adp94xx and aic94xx on my 9405W) but if anybody knows better,
please enlighten me. :)

That said, the effect of leaving these values set to 1 is terrible
performance in the case of either (a) certain Maxtor SAS drives flying
solo or (b) flooding several disks with I/O simultaneously (md-raid).
There may be more scenarios where we see similar problems that I
haven't uncovered.

Just for grins, I ran bogodisk (an O_DIRECT-enabled read speed test)
against three different scenarios:

1) adp94xx 1.0.8-6, pounded into 2.6.18-rc4 [green]
2) aic94xx 1.0.2, without this patch        [red]
3) aic94xx 1.0.2, with this                 [blue]

...with these results:

http://sweaglesw.net/~djwong/programs/bogodisk/bd_graphs/bad_sas.0.png

As you can see, the read performance is cut in half by the aic94xx
driver not getting a chance to have multiple I/Os in flight at any given 
time.  With the patch, the two drivers are fairly close bandwidth-wise.
Also thanks to Mike Anderson for helping me figure this out.

--D

Signed-off-by: Darrick J. Wong <djwong@us.ibm.com>

diff --git a/drivers/scsi/aic94xx/aic94xx_hwi.h b/drivers/scsi/aic94xx/aic94xx_hwi.h
index c7d5053..a2d8881 100644
--- a/drivers/scsi/aic94xx/aic94xx_hwi.h
+++ b/drivers/scsi/aic94xx/aic94xx_hwi.h
@@ -36,6 +36,9 @@
 #include "aic94xx.h"
 #include "aic94xx_sas.h"
 
+/* Leave a few empty data buffers. */
+#define ASD_FREE_SCBS      3
+
 /* Define ASD_MAX_PHYS to the maximum phys ever. Currently 8. */
 #define ASD_MAX_PHYS       8
 #define ASD_PCBA_SN_SIZE   12
diff --git a/drivers/scsi/aic94xx/aic94xx_init.c b/drivers/scsi/aic94xx/aic94xx_init.c
index 3ec2e46..34a7b4b 100644
--- a/drivers/scsi/aic94xx/aic94xx_init.c
+++ b/drivers/scsi/aic94xx/aic94xx_init.c
@@ -71,7 +72,7 @@ static struct scsi_host_template aic94xx
 	.change_queue_type	= sas_change_queue_type,
 	.bios_param		= sas_bios_param,
 	.can_queue		= 1,
-	.cmd_per_lun		= 1,
+	.cmd_per_lun		= 2,
 	.this_id		= -1,
 	.sg_tablesize		= SG_ALL,
 	.max_sectors		= SCSI_DEFAULT_MAX_SECTORS,
@@ -612,13 +616,17 @@ static int __devinit asd_pci_probe(struc
 		goto Err_free_cache;
 
 	asd_printk("device %s: SAS addr %llx, PCBA SN %s, %d phys, %d enabled "
-		   "phys, flash %s, BIOS %s%d\n",
+		   "phys, flash %s, BIOS %s%d, SCBs %d\n",
 		   pci_name(dev), SAS_ADDR(asd_ha->hw_prof.sas_addr),
 		   asd_ha->hw_prof.pcba_sn, asd_ha->hw_prof.max_phys,
 		   asd_ha->hw_prof.num_phys,
 		   asd_ha->hw_prof.flash.present ? "present" : "not present",
 		   asd_ha->hw_prof.bios.present ? "build " : "not present",
-		   asd_ha->hw_prof.bios.bld);
+		   asd_ha->hw_prof.bios.bld,
+		   asd_ha->hw_prof.max_scbs);
+
+	aic94xx_sht.can_queue = asd_ha->hw_prof.max_scbs - ASD_FREE_SCBS;
+	shost->can_queue = aic94xx_sht.can_queue;
 
 	if (use_msi)
 		pci_enable_msi(asd_ha->pcidev);