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SubjectRe: performance drop after using blkcg
From
2012/12/11 Vivek Goyal <vgoyal@redhat.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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