linux-kernel - [PATCH v3] aic94xx: Increase can

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Date:	Wed, 30 Aug 2006 13:55:48 -0700
From:	"Darrick J. Wong" <djwong@...ibm.com>
To:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-scsi@...r.kernel.org, Alexis Bruemmer <alexisb@...ibm.com>,
	Mike Anderson <andmike@...ibm.com>,
	Konrad Rzeszutek <konrad@...nok.org>
Subject: [PATCH v3] aic94xx: Increase can_queue for better performance

Hi all,

Below is a patch that sets can_queue in the aic94xx driver's scsi_host
to better performing values than what's there currently.  It seems that
asd_ha->seq.can_queue reflects the number of requests that can be
queued per controller; so long as there's one scsi_host per controller,
it seems logical that the scsi_host ought to have the same can_queue
value.  To the best of my (still limited) knowledge, this method
provides the correct value.

The effect of leaving this value 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.

--D

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

diff --git a/drivers/scsi/aic94xx/aic94xx_init.c b/drivers/scsi/aic94xx/aic94xx_init.c
index 3e25e31..5c6d457 100644
--- a/drivers/scsi/aic94xx/aic94xx_init.c
+++ b/drivers/scsi/aic94xx/aic94xx_init.c
@@ -623,6 +623,8 @@ static int __devinit asd_pci_probe(struc
                   asd_ha->hw_prof.bios.present ? "build " : "not present",
                   asd_ha->hw_prof.bios.bld);

+       shost->can_queue = asd_ha->seq.can_queue;
+
        if (use_msi)
                pci_enable_msi(asd_ha->pcidev);

-
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