linux-kernel - Re: [PATCH 0/6 v5.1] cfq-iosched: Introduce CFQ group hierarchical scheduling and "use

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Date:	Mon, 7 Mar 2011 10:07:12 -0800
From:	Justin TerAvest <teravest@...gle.com>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	Gui Jianfeng <guijianfeng@...fujitsu.com>,
	Jens Axboe <axboe@...nel.dk>,
	"jmoyer@...hat.com" <jmoyer@...hat.com>,
	Chad Talbott <ctalbott@...gle.com>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/6 v5.1] cfq-iosched: Introduce CFQ group hierarchical
 scheduling and "use_hierarchy" interface

On Mon, Mar 7, 2011 at 6:28 AM, Vivek Goyal <vgoyal@...hat.com> wrote:
> On Sat, Mar 05, 2011 at 01:16:08PM +0800, Gui Jianfeng wrote:
>
> [..]
>> >> This bug seems being introduced in commmit 763414b in for-next branch when
>> >> merging for-2.6.39/core branch.
>> >> Would you apply the above patch?
>> >>
>> >> Vivek, can you try the patchset again with this fix? It works fine for me now.
>> >
>> > Gui,
>> >
>> > Ok, I ran iostest with this fix and it seems to have worked. I need to run
>> > it for some more time. And I also need to spend more time reviewing your
>> > patchset. There are so many details to it. Soon I will spare some time
>> > to review it more and also test it bit more.
>>
>> Vivek,
>>
>> Ok, thanks.
>>
>> >
>> > Of the top of my head I have one concern.
>> >
>> > - How to map iopriority to weights. I am thinking that currently weight
>> >   range is 100-1000. If we decide to extend the range in current scheme,
>> >   it will change the ioprio entity weight also and effectively the
>> >   service differentiation between ioprio level will change. I am
>> >   wondering if this is a concern and how cpu scheduler has managed it
>>
>> Isn't it enought for ten times of weight difference? The old ioprio scheme
>> has only 4.5 times service difference. So I think we don't need to extend
>> the range for the time being.
>
> Well, never say never. I think google guys are already using minimum
> weight of 10. So don't rule it out.

Yes, we're using a minimum weight of 10. We still see good isolation with
the minimum that low.

Thanks,
Justin

>
> Secondly, because we might not idle all the time the effective service
> differentiation might be much less than a factor of 10. In that case
> to get effective 10, one might have to go for wider range of weights.
>
> Thanks
> Vivek
>
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