linux-kernel - Re: performance drop after using blkcg

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Date:	Wed, 12 Dec 2012 15:29:55 +0800
From:	Zhao Shuai <zhaoshuai@...ebsd.org>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	tj@...nel.org, axboe@...nel.dk, ctalbott@...gle.com,
	rni@...gle.com, linux-kernel@...r.kernel.org,
	cgroups@...r.kernel.org, containers@...ts.linux-foundation.org
Subject: Re: performance drop after using blkcg

2012/12/11 Vivek Goyal <vgoyal@...hat.com>:
> These results are with slice_idle=0?

Yes, slice_idle is disabled.

> What's the storage you are using. Looking at the speed of IO I would
> guess it is not one of those rotational disks.

I have done the same test on 3 different type of boxes,and all of them
show a performance drop(30%-40%) after using blkcg. Though they
have different type of disk, all the storage they use are traditional
rotational
devices(e.g."HP EG0146FAWHU", "IBM-ESXS").

> So if somebody wants to experiment, just tweak the code a bit to allow
> preemption when a queue which lost share gets backlogged and you
> practially have a prototype of iops based group scheduling.

Could you please explain more on this? How to adjust the code? I have test
the following code piece, the result is we lost group differentiation.

cfq_group_served() {
         if (iops_mode(cfqd))
                 charge = cfqq->slice_dispatch;
         cfqg->vdisktime += cfq_scale_slice(charge, cfqg);
 }


-- 
Regards,
Zhao Shuai
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