linux-kernel - Re: The difference of request dir between AS and Deadline I/O scheduler?

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Message-ID: <20090302122547.GT11787@kernel.dk>
Date:	Mon, 2 Mar 2009 13:25:48 +0100
From:	Jens Axboe <jens.axboe@...cle.com>
To:	???? <xiegang112@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: The difference of request dir between AS and Deadline I/O
	scheduler?

On Mon, Mar 02 2009, ???? wrote:
> Hi,
> 
> I'm little confused about the defination of request dir in AS and
> Deadline I/O scheduler.
> In AS, the request dir is defined by wheher it's sync:
> 
> data_dir = rq_is_sync(rq);
> 
> But in Deadline, the requests are grouped by read and write.
> 
> Why is there the difference since AS is an extension of Deadline?
> what's the consideration?

Because AS uses the sync vs async distinction to decide whether to
anticipate a new request from that process. 'sync' is then reads or sync
writes, whereas deadline does not distinguish between sync and async
writes.

-- 
Jens Axboe

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