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

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Message-ID: <20061219112649.GG5010@kernel.dk>
Date:	Tue, 19 Dec 2006 12:26:49 +0100
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Arjan van de Ven <arjan@...rus.demon.nl>
Cc:	Dan Aloni <da-x@...atomic.org>,
	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

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.

-- 
Jens Axboe

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