Groups > linux.kernel > #1445497 > unrolled thread

Cgroup: iops throttle problem

Started by	张真 <zhangzhen507@163.com>
First post	2016-07-18 16:00 +0200
Last post	2016-07-20 17:40 +0200
Articles	2 — 2 participants

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  Cgroup: iops throttle problem 张真 <zhangzhen507@163.com> - 2016-07-18 16:00 +0200
    Re: Cgroup: iops throttle problem Tejun Heo <tj@kernel.org> - 2016-07-20 17:40 +0200

#1445497 — Cgroup: iops throttle problem

From	张真 <zhangzhen507@163.com>
Date	2016-07-18 16:00 +0200
Subject	Cgroup: iops throttle problem
Message-ID	<rWhfr-6UE-9@gated-at.bofh.it>

Hello
My name is Zhen Zhang , me and Jiale Li recently test and analyze the cgroup
blkio functions.
We tested the buffered read a file using bio when the 
blkio.throttle.read_iops_device is set 1000.
The fio result file displays the iops is 13720 larger than 1000 when blocksize 
is 4K in fio.

We set different blocksize in fio:
4K, 8K , 16K, 32K, 64K, 128K, 256K, 512K, 1024K

The iops in fio:
13035, 7258, 3711, 1698, 907, 460, 228, 102, 54
When bs is less than 64K, the iops is larger than 1000, when bs is larger than
64K, the iops is less than 1000.
We tested it on ubuntu 16.04 with kernel 4.4.0

Dose this a problem of blkio iops throttle?

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#1447300

From	Tejun Heo <tj@kernel.org>
Date	2016-07-20 17:40 +0200
Message-ID	<rX1Lj-3cG-1@gated-at.bofh.it>
In reply to	#1445497

Hello,

On Mon, Jul 18, 2016 at 09:35:12PM +0800, 张真 wrote:
> Hello
> My name is Zhen Zhang , me and Jiale Li recently test and analyze the cgroup
> blkio functions.
> We tested the buffered read a file using bio when the 
> blkio.throttle.read_iops_device is set 1000.
> The fio result file displays the iops is 13720 larger than 1000 when blocksize 
> is 4K in fio.

blk-throttle does allow bursts so the iops might go over the set limit
for a short period.  Over time, it shouldn't be over the set limit.

> We set different blocksize in fio:
> 4K, 8K , 16K, 32K, 64K, 128K, 256K, 512K, 1024K
> 
> The iops in fio:
> 13035, 7258, 3711, 1698, 907, 460, 228, 102, 54

Looks like you were hitting the natural bandwidth limit of the device.

> When bs is less than 64K, the iops is larger than 1000, when bs is larger than
> 64K, the iops is less than 1000.
> We tested it on ubuntu 16.04 with kernel 4.4.0
> 
> Dose this a problem of blkio iops throttle?

I don't know how the test was run but consistently going over the set
limit isn't the expected behavior.

Thanks.

-- 
tejun

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#1445497 — Cgroup: iops throttle problem

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