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

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Date:	Wed, 16 Feb 2011 09:06:14 +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 Tue, Feb 15, 2011 at 09:53:58AM +0800, Gui Jianfeng wrote:
>> 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.
> 
> Ok, that makes sense. So as suggested in other mails, lets use a even
> smaller base so that freshly backlogged queues get smaller vdisktimes
> as compared to existing queues which are using disks for longer time.

Ok, It sounds making sense.

Thanks
Gui

> 
> Thanks
> Vivek
> 
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