Re: [PATCH] 2.5 current bk fix setting scsi queue depths

[Patrick Mansfield <patmans@us.ibm.com>]

On Wed, Oct 30, 2002 at 11:17:52AM -0600, James Bottomley wrote:
> patmans@us.ibm.com said:
> > This patch fixes a problem with the current linus bk tree setting scsi
> > queue depths to 1. Please apply. 
> 
> This patch causes the depth specification to be retained when we release 
> commandblocks.  Since releasing command blocks is supposed only to be done 
> when we give up the device (and therefore, is supposed to clear everything), 
> your fix looks like it's merely masking a problem, not fixing it.
> 
> Is the real problem that this controller is getting a release command blocks 
> and then a reallocate of them after slave_attach is called?  If so, that's 
> probably what needs to be fixed.
> 
> James

Yes, the problem is that in scsi_register_host() if there are no upper
level drivers - the standard case if building no modules - we call
scsi_release_commandblocks even though we are NOT getting rid of
the scsi_device. So, with current code, new_queue_depth and
current_queue_depth are zero.

When we register upper level drivers in scsi_register_device(), we
call scsi_build_commandblocks (again), and get a queue depth of 1,
since we've cleared new_queue_depth.

(In many cases, for one device we call build command blocks twice, call
release command blocks, and then build command blocks again. Yuck)

Removing the scsi_release_commandblocks() in scsi_register_host()
would also fix the problem, and in most cases, would not waste any
space. In the worst case AFAICT it would waste one scsi_cmnd (about 300
or so bytes?).

I see no good reason to zero new_queue_depth in scsi_release_commandblocks,
as new_queue_depth is the desired queue depth, and should remain so until
scsi_adjust_queue_depth is called. Setting new_queue_depth to zero means
we have to call slave_attach again to set it right, and depending on what
else an adapter slave_attach does could be very wrong.

-- Patrick Mansfield