linux-kernel - Re: [PATCH 3/6 v4] cfq-iosched: Introduce vdisktime and io weight for CFQ queue

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Date:	Tue, 15 Feb 2011 09:53:58 +0800
From:	Gui Jianfeng <guijianfeng@...fujitsu.com>
To:	Vivek Goyal <vgoyal@...hat.com>
CC:	Jens Axboe <axboe@...nel.dk>, Shaohua Li <shaohua.li@...el.com>,
	lkml <linux-kernel@...r.kernel.org>,
	Chad Talbott <ctalbott@...gle.com>,
	Divyesh Shah <dpshah@...gle.com>
Subject: Re: [PATCH 3/6 v4] cfq-iosched: Introduce vdisktime and io weight
 for CFQ queue

Vivek Goyal wrote:
> On Sat, Feb 12, 2011 at 09:20:58AM +0800, Gui Jianfeng wrote:
>> Vivek Goyal wrote:
>>> On Thu, Feb 10, 2011 at 03:47:16PM +0800, Gui Jianfeng wrote:
>>>> Introduce vdisktime and io weight for CFQ queue scheduling. Currently, io priority
>>>> maps to a range [100,1000]. It also gets rid of cfq_slice_offset() logic and makes
>>>> use the same scheduling algorithm as CFQ group does. This helps for CFQ queue and
>>>> group scheduling on the same service tree.
>>>>
>>>> Signed-off-by: Gui Jianfeng <guijianfeng@...fujitsu.com>
>>>> ---
>>>>  block/cfq-iosched.c |  219 +++++++++++++++++++++++++++++++++++++++------------
>>>>  1 files changed, 167 insertions(+), 52 deletions(-)
>>>>
>>>> diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
>>>> index f3a126e..41cef2e 100644
>>>> --- a/block/cfq-iosched.c
>>>> +++ b/block/cfq-iosched.c
>>>> @@ -39,6 +39,13 @@ static const int cfq_hist_divisor = 4;
>>>>   */
>>>>  #define CFQ_IDLE_DELAY		(HZ / 5)
>>>>  
>>>> +/* 
>>>> + * The base boosting value.
>>>> + */
>>>> +#define CFQ_BOOST_SYNC_BASE          (HZ / 10)
>>>> +#define CFQ_BOOST_ASYNC_BASE          (HZ / 25)
>>>> +
>>> These are same as cfq_slice_sync and cfq_slice_async. Looking at
>>> boost logic, this is equivalent of starting a new queue/group as
>>> if it is being requeued after conuming a full slice. So may be we can divide
>>> it by some const number say 4 or something like that. This is a minor
>>> point though as this algorimthm will kind of evolve and we will learn
>>> what works best.
>>>
>>> Secondly, I think you wanted to SYNC vs ASYNC logic seem to be reversed.
>>> We would like to give ASYNC queues higher boost (Put these farther in 
>>> tree) and lesser boost to SYNC queues. Looks like above constants will
>>> do the reverse? 
>> Hi Vivek,
>>
>> Currently, SYNC and ASYNC queues are in different service tree, they don't
>> impact each other. Here, I Really want use this logic.
> 
> Ok, SYNC and ASYNC are on separate service tree so their vtime are not
> comparable (as of today, down the line one might want to look at those for
> better workload selection logic).
> 
> Anyway, because two are on seprate tree so why should we have separate
> boosting constants for them? How does it help?

Here if we are using CFQ_BOOST_SYNC_BASE for both, I think it might boost
too much for an ASYNC cfqe as compare to others on the same service tree(async).
So I make charging and boosting follow the same base.

Thanks,
Gui

> 
> Thanks
> Vivek
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