Re: Buffered I/O to block device very slow and other SCSI issues...

[Jeremy Higdon <jeremy@sgi.com>]

On Thu, Mar 20, 2008 at 10:16:54AM +1100, David Chinner wrote:
> 4p ia64, 24GB RAM, 2.6.25-rc3, qla1280, 15krpm scsi disk.
> 
> Direct I/O:
> 
> dgc@budgie:~/xfstests$ sudo dd if=/dev/zero of=/dev/sdb6 bs=1024k count=1024 oflag=direct
> 1024+0 records in
> 1024+0 records out
> 1073741824 bytes (1.1 GB) copied, 27.8974 s, 38.5 MB/s
> 
> Doing approximately 80 512k I/os per second (disk bandwidth).
> 
> Buffered I/O:
> 
> dgc@budgie:~/xfstests$ sudo dd if=/dev/zero of=/dev/sdb6 bs=1024k count=4096
> 4096+0 records in
> 4096+0 records out
> 4294967296 bytes (4.3 GB) copied, 427.872 s, 10.0 MB/s

How big is sdb6?  How many '2's do you see in

	factor `cat /sys/block/sdb/sdb6/size`

> 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.

jeremy