Re: [PATCH] ieee1394: sbp2: lower block queue alignment requirement

[Stefan Richter <stefanr@s5r6.in-berlin.de>]

On 14 Jan, James Bottomley wrote:
> The block layer currently provides sector (512) byte alignment
> guarantees.  However, there has been talk in SCSI of reducing that to
> word (4) since that's what most intelligent PCI controllers can cope
> with.  If you have any alignment constraints, they should be expressed
> in the slave configure.


From: Stefan Richter <stefanr@s5r6.in-berlin.de>
Subject: [PATCH update] ieee1394: sbp2: lower block queue alignment requirement

The old setting is copy & waste from usb-storage and doesn't apply to
sbp2.  There is only 4-byte alignment required for everything, except
for S/G table elements which have to be 8-byte aligned according to the
SBP-2 spec.  (They happen to be ____cacheline_aligned in our
implementation.  Whether that's good is another question.)

We now simply don't tune block queue alignment at all.  The default
alignment would surely never become anything else than a multiple of 4,
else tons of calls to blk_queue_dma_alignment would have to be added
everywhere in drivers/...

Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
---
Index: linux-2.6.20-rc5/drivers/ieee1394/sbp2.c
===================================================================
--- linux-2.6.20-rc5.orig/drivers/ieee1394/sbp2.c
+++ linux-2.6.20-rc5/drivers/ieee1394/sbp2.c
@@ -51,7 +51,6 @@
  * Grep for inline FIXME comments below.
  */
 
-#include <linux/blkdev.h>
 #include <linux/compiler.h>
 #include <linux/delay.h>
 #include <linux/device.h>
@@ -2012,7 +2011,6 @@ static int sbp2scsi_slave_configure(stru
 {
 	struct sbp2_lu *lu = (struct sbp2_lu *)sdev->host->hostdata[0];
 
-	blk_queue_dma_alignment(sdev->request_queue, (512 - 1));
 	sdev->use_10_for_rw = 1;
 
 	if (sdev->type == TYPE_ROM)



-- 
Stefan Richter
-=====-=-=== ---= ==--=
http://arcgraph.de/sr/


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