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Date: Mon, 30 Sep 2002 10:15:22 +0200
From: Jens Axboe <axboe@suse.de>
To: Andrew Morton <akpm@digeo.com>,
       Linux Kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] deadline io scheduler
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On Thu, Sep 26 2002, Patrick Mansfield wrote:
> On Thu, Sep 26, 2002 at 08:59:51AM +0200, Jens Axboe wrote:
> > On Thu, Sep 26 2002, Jens Axboe wrote:
> > BTW, for SCSI, it would be nice to first convert more drivers to use the
> > block level queued tagging. That would provide us with a much better
> > means to control starvation properly on SCSI as well.
> > 
> > -- 
> > Jens Axboe
> 
> I haven't look closely at the block tagging, but for the FCP protocol,
> there are no tags, just the type of queueing to use (task attributes)
> - like ordered, head of queue, untagged, and some others. The tagging
> is normally done on the adapter itself (FCP2 protocol AFAIK). Does this
> mean block level queued tagging can't help FCP?

The generic block level tagging is nothing more than tag management. It
can 'tag' a request (assigning it an integer tag), and later let you
locate that request by giving it the tag.

I suspect you need none of that for FCP. Instead it looks more like you
can set the task attributes based on the type of request itself. So you
would currently set 'ordered' for a request with REQ_BARRIER set. And
you could set 'head of queue' for REQ_URGENT (I'm making this one up
:-), etc.

Do you need any request management to deal with FCP queueing? It doesn't
sound like it.

-- 
Jens Axboe

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