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

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Message-ID: <d364733c0903020503x43a1448cq1b127a88fd816e1c@mail.gmail.com>
Date:	Mon, 2 Mar 2009 21:03:25 +0800
From:	谢纲 <xiegang112@...il.com>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: The difference of request dir between AS and Deadline I/O 
	scheduler?

Do you mean that the same process tends to have the same behavior of
I/O in the way of sycn?
Does this mean AS works better when requests are distincted by sync
mode  (the success rate of anticipation is higher when requests are
grouped by the mode of sync)?

Thanks,


On Mon, Mar 2, 2009 at 8:25 PM, Jens Axboe <jens.axboe@...cle.com> wrote:
> 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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