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

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Message-ID: <458830B9.90107@dresco.co.uk>
Date:	Tue, 19 Dec 2006 18:34:33 +0000
From:	Jon Escombe <lists@...sco.co.uk>
To:	Jens Axboe <jens.axboe@...cle.com>
CC:	Arjan van de Ven <arjan@...rus.demon.nl>,
	Dan Aloni <da-x@...atomic.org>,
	Linux Kernel List <linux-kernel@...r.kernel.org>,
	linux-scsi@...r.kernel.org, Mike Christie <michaelc@...wisc.edu>,
	Elias Oltmanns <eo@...ensachen.de>
Subject: Re: [PATCH] scsi_execute_async() should add to the tail of the  queue

Jens Axboe wrote:
 > On Tue, Dec 19 2006, Arjan van de Ven wrote:
 >> On Tue, 2006-12-19 at 10:35 +0200, 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.
 >> Hi,
 >>
 >> some things should really be added to the head of the queue, like
 >> maintenance requests and error handling requests. Are you sure this is
 >> the right change? At least I'd expect 2 apis, one for a head and one for
 >> a "normal" queueing...
 >
 > It does sounds broken - head insertion should only be used for careful
 > internal commands, not be the default way user issued commands. Looking
 > at the current users, the patch makes sense to me.
 >

It's worth noting that the hdaps disk protection patches rely on the 
current behaviour to add 'IDLE IMMEDIATE WITH UNLOAD' commands to the 
head of the queue.. Another function, or a new parameter for queue 
position would be needed to retain this functionality - any preference 
for either?

Regards,
Jon.

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