linux-kernel - Re: [PATCH] scsi_execute_async() should add to the tail of the queue

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Date:	Wed, 20 Dec 2006 20:40:29 +0000
From:	Steven Hayter <steven@...ter.me.uk>
To:	Dan Aloni <da-x@...atomic.org>
CC:	Linux Kernel List <linux-kernel@...r.kernel.org>,
	linux-scsi@...r.kernel.org, Mike Christie <michaelc@...wisc.edu>
Subject: Re: [PATCH] scsi_execute_async() should add to the tail of the queue

Dan Aloni wrote:
> Hello,
> 
> scsi_execute_async() has replaced scsi_do_req() a few versions ago, 
> but it also incurred a change of behavior. I noticed that over-queuing 
> a SCSI device using that function causes I/Os to be starved from 
> low-level queuing for no justified reason.
>  
> I think it makes much more sense to perserve the original behaviour 
> of scsi_do_req() and add the request to the tail of the queue.

As far as I'm aware the way in which scsi_do_req() was to insert at the 
head of the queue, leading to projects like SCST to come up with 
scsi_do_req_fifo() as queuing multiple commands using scsi_do_req() with 
constant head insertion might lead to out of order execution.

Just thought I'd throw some light on the history and what others have 
done in the past.

Steve
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