Re: [RFC PATCH] cfq-iosced: Implement IOPS mode and group_idle tunable V3

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

Vivek Goyal wrote:
> On Thu, Jul 22, 2010 at 03:08:00PM +0800, Gui Jianfeng wrote:
>> Vivek Goyal wrote:
>>> Hi,
>>>
>>> This is V3 of the group_idle and CFQ IOPS mode implementation patchset. Since V2
>>> I have cleaned up the code a bit to clarify the confusion lingering around in
>>> what cases do we charge time slice and in what cases do we charge number of
>>> requests.
>>>
>>> What's the problem
>>> ------------------
>>> On high end storage (I got on HP EVA storage array with 12 SATA disks in 
>>> RAID 5), CFQ's model of dispatching requests from a single queue at a
>>> time (sequential readers/write sync writers etc), becomes a bottleneck.
>>> Often we don't drive enough request queue depth to keep all the disks busy
>>> and suffer a lot in terms of overall throughput.
>>>
>>> All these problems primarily originate from two things. Idling on per
>>> cfq queue and quantum (dispatching limited number of requests from a
>>> single queue) and till then not allowing dispatch from other queues. Once
>>> you set the slice_idle=0 and quantum to higher value, most of the CFQ's
>>> problem on higher end storage disappear.
>>>
>>> This problem also becomes visible in IO controller where one creates
>>> multiple groups and gets the fairness but overall throughput is less. In
>>> the following table, I am running increasing number of sequential readers
>>> (1,2,4,8) in 8 groups of weight 100 to 800.
>>>
>>> Kernel=2.6.35-rc5-iops+
>>> GROUPMODE=1          NRGRP=8
>>> DIR=/mnt/iostestmnt/fio        DEV=/dev/dm-4
>>> Workload=bsr      iosched=cfq     Filesz=512M bs=4K
>>> group_isolation=1 slice_idle=8    group_idle=8    quantum=8
>>> =========================================================================
>>> AVERAGE[bsr]    [bw in KB/s]
>>> -------
>>> job     Set NR  cgrp1  cgrp2  cgrp3  cgrp4  cgrp5  cgrp6  cgrp7  cgrp8  total
>>> ---     --- --  ---------------------------------------------------------------
>>> bsr     3   1   6186   12752  16568  23068  28608  35785  42322  48409  213701
>>> bsr     3   2   5396   10902  16959  23471  25099  30643  37168  42820  192461
>>> bsr     3   4   4655   9463   14042  20537  24074  28499  34679  37895  173847
>>> bsr     3   8   4418   8783   12625  19015  21933  26354  29830  36290  159249
>>>
>>> Notice that overall throughput is just around 160MB/s with 8 sequential reader
>>> in each group.
>>>
>>> With this patch set, I have set slice_idle=0 and re-ran same test.
>>>
>>> Kernel=2.6.35-rc5-iops+
>>> GROUPMODE=1          NRGRP=8
>>> DIR=/mnt/iostestmnt/fio        DEV=/dev/dm-4
>>> Workload=bsr      iosched=cfq     Filesz=512M bs=4K
>>> group_isolation=1 slice_idle=0    group_idle=8    quantum=8
>>> =========================================================================
>>> AVERAGE[bsr]    [bw in KB/s]
>>> -------
>>> job     Set NR  cgrp1  cgrp2  cgrp3  cgrp4  cgrp5  cgrp6  cgrp7  cgrp8  total
>>> ---     --- --  ---------------------------------------------------------------
>>> bsr     3   1   6523   12399  18116  24752  30481  36144  42185  48894  219496
>>> bsr     3   2   10072  20078  29614  38378  46354  52513  58315  64833  320159
>>> bsr     3   4   11045  22340  33013  44330  52663  58254  63883  70990  356520
>>> bsr     3   8   12362  25860  37920  47486  61415  47292  45581  70828  348747
>>>
>>> Notice how overall throughput has shot upto 348MB/s while retaining the ability
>>> to do the IO control.
>>>
>>> So this is not the default mode. This new tunable group_idle, allows one to
>>> set slice_idle=0 to disable some of the CFQ features and and use primarily
>>> group service differentation feature.
>>>
>>> If you have thoughts on other ways of solving the problem, I am all ears
>>> to it.
>> Hi Vivek
>>
>> Would you attach your fio job config file?
>>
> 
> Hi Gui,
> 
> I have written a fio based test script, "iostest", to be able to
> do cgroup and other IO scheduler testing more smoothly and I am using
> that. I am attaching the compressed script with the mail. Try using it
> and if it works for you and you find it useful, I can think of hosting a
> git tree somewhere.
> 
> I used following following command lines to test above.
> 
> # iostest <block-device> -G -w bsr -m 8 -c --nrgrp 8 --total
> 
> With slice idle disabled.
> 
> # iostest <block-device> -G -w bsr -m 8 -c --nrgrp 8 --total -I 0

That's cool! Very helpful, I'll try it.

Thanks,
Gui

> 
> Thanks
> Vivek

-- 
Regards
Gui Jianfeng