Re: [PATCH 0/6 v4] cfq-iosched: Introduce CFQ group hierarchical scheduling and "use_hierarchy" interface

[Gui Jianfeng <guijianfeng@cn.fujitsu.com>]

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?

Hi Vivek,

I did fio test by runing 8 threads with different ioprio. It seems patched kernel
and vanilla kernel act the same behaviour. That is it doesn't play well. As I metioned
in previous mail, when I disable idling, all threads become SYNC_NOIDLE, and then
preempt each other, even if I start 8 threads. And reposition at the top of service
tree. This's why we can't see service differetiation.

> 
> 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.
> 
> 	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.

Ok, I'd like to take a look chad's patch.

Thanks
Gui
> 
> Thanks
> Vivek
>