linux-kernel - Re: [PATCH 0/6 v4] cfq-iosched: Introduce CFQ group hierarchical scheduling and "use

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Message-ID: <4D5623F6.7020101@cn.fujitsu.com>
Date:	Sat, 12 Feb 2011 14:08:54 +0800
From:	Gui Jianfeng <guijianfeng@...fujitsu.com>
To:	Vivek Goyal <vgoyal@...hat.com>, Chad Talbott <ctalbott@...gle.com>
CC:	Jens Axboe <axboe@...nel.dk>, Shaohua Li <shaohua.li@...el.com>,
	lkml <linux-kernel@...r.kernel.org>,
	Divyesh Shah <dpshah@...gle.com>
Subject: Re: [PATCH 0/6 v4] cfq-iosched: Introduce CFQ group hierarchical
 scheduling and "use_hierarchy" interface

Vivek Goyal wrote:
> On Thu, Feb 10, 2011 at 03:45:45PM +0800, Gui Jianfeng wrote:
>> Hi
>>
>> Previously, I posted a patchset to add support of CFQ group hierarchical scheduling
>> in the way that it puts all CFQ queues in a hidden group and schedules with other 
>> CFQ group under their parent. The patchset is available here,
>> http://lkml.org/lkml/2010/8/30/30
>>
>> Vivek think this approach isn't so instinct that we should treat CFQ queues
>> and groups at the same level. Here is the new approach for hierarchical 
>> scheduling based on Vivek's suggestion. The most big change of CFQ is that
>> it gets rid of cfq_slice_offset logic, and makes use of vdisktime for CFQ
>> queue scheduling just like CFQ group does. But I still give cfqq some jump 
>> in vdisktime based on ioprio, thanks for Vivek to point out this. Now CFQ 
>> queue and CFQ group use the same scheduling algorithm. 
>>
>> "use_hierarchy" interface is now added to switch between hierarchical mode
>> and flat mode. It works as memcg.
>>
>> --
>> V3 -> V4 Changes:
>> - Take io class into account when calculating the boost value.
>> - Refine the vtime boosting logic as Vivek's Suggestion.
> 
> Hi Gui,
> 
> What testing did you do to make sure that this vtime boosting logic is working
> and is good replacement for slice_offset() logic for cfqq?
> 
> Secondly, did you get a chance to look at chad's patch of keeping track
> of previous assigned vdisktime and keeping track of genrations. I think
> his patch is going to coflict with yours, so one of you will have to
> make adjustments. I think both the boost logic and keeping track of generation
> logic can be combined.

Hi Vivek,

For the time being, boosting logic only works for cfq queue, and keepinging track of
generation works for cfq group.
I think when we introduce boosting logic for cfq group, we can combine these two logic
together.

Thanks,
Gui

> 
> 	if (entity->gneration_number > cfqd->active_generation)
> 		Use_boost_logic;
> 	else
> 		Use_previously_assigned_vdisktime;
> 
> 
> That way if we generation has changed then we really don't have a valid
> vdisktime and we can use boost logic to come up with differential
> vdisktime and if generation has not changed then we can continue to make
> use of previous vdisktime.
> 
> Thanks
> Vivek
> --
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