linux-kernel - Re: request to revert libata-convert-to-block-tagging patches

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Message-ID: <4917C6DD.4010500@kernel.org>
Date:	Mon, 10 Nov 2008 14:30:05 +0900
From:	Tejun Heo <tj@...nel.org>
To:	Jens Axboe <jens.axboe@...cle.com>, Jeff Garzik <jeff@...zik.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	IDE/ATA development list <linux-ide@...r.kernel.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: request to revert libata-convert-to-block-tagging patches

Tejun Heo wrote:
> #1 is easy to fix but #2 requires either adding a spinlock or two atomic
> variables to struct blk_queue_tag to keep the current behavior while
> guaranteeing that tags are used in order.  Also, there's delay between
> libata marks a request complete and the request actually gets completed
> and the tag is freed.  If another request gets issued inbetween, the tag
> number can't be guaranteed.  This can be worked around by re-mapping tag
> number in libata depending on command type but, well then, it's worse
> than the original implementation.

I think this can be made to work by making tag free synchronous (ie.
doing it when the request is passed over to softirq) but I don't think
things like that should go into 2.6.28 at this point.

Thanks.

-- 
tejun
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