linux-kernel - Re: [PATCH 01/20] blkio: Documentation

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Date:	Wed, 4 Nov 2009 22:51:00 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	linux-kernel@...r.kernel.org, jens.axboe@...cle.com,
	nauman@...gle.com, dpshah@...gle.com, lizf@...fujitsu.com,
	ryov@...inux.co.jp, fernando@....ntt.co.jp, s-uchida@...jp.nec.com,
	taka@...inux.co.jp, guijianfeng@...fujitsu.com, jmoyer@...hat.com,
	righi.andrea@...il.com, m-ikeda@...jp.nec.com,
	akpm@...ux-foundation.org, riel@...hat.com,
	kamezawa.hiroyu@...fujitsu.com
Subject: Re: [PATCH 01/20] blkio: Documentation

* Vivek Goyal <vgoyal@...hat.com> [2009-11-03 18:43:38]:

> Signed-off-by: Vivek Goyal <vgoyal@...hat.com>
> ---
>  Documentation/cgroups/blkio-controller.txt |  106 ++++++++++++++++++++++++++++
>  1 files changed, 106 insertions(+), 0 deletions(-)
>  create mode 100644 Documentation/cgroups/blkio-controller.txt
> 
> diff --git a/Documentation/cgroups/blkio-controller.txt b/Documentation/cgroups/blkio-controller.txt
> new file mode 100644
> index 0000000..dc8fb1a
> --- /dev/null
> +++ b/Documentation/cgroups/blkio-controller.txt
> @@ -0,0 +1,106 @@
> +				Block IO Controller
> +				===================
> +Overview
> +========
> +cgroup subsys "blkio" implements the block io controller. There seems to be
> +a need of various kind of IO control policies (like proportional BW, max BW)
> +both at leaf nodes as well as at intermediate nodes in storage hierarchy. Plan
> +is to use same cgroup based management interface for blkio controller and
> +based on user options switch IO policies in the background.
> +
> +In the first phase, this patchset implements proportional weight time based
> +division of disk policy. It is implemented in CFQ. Hence this policy takes
> +effect only on leaf nodes when CFQ is being used.
> +
> +HOWTO
> +=====
> +You can do a very simple testing of running two dd threads in two different
> +cgroups. Here is what you can do.
> +
> +- Enable group scheduling in CFQ
> +	CONFIG_CFQ_GROUP_IOSCHED=y
> +
> +- Compile and boot into kernel and mount IO controller (blkio).
> +
> +	mount -t cgroup -o blkio none /cgroup
> +
> +- Create two cgroups
> +	mkdir -p /cgroup/test1/ /cgroup/test2
> +
> +- Set weights of group test1 and test2
> +	echo 1000 > /cgroup/test1/blkio.weight
> +	echo 500 > /cgroup/test2/blkio.weight
> +
> +- Create two same size files (say 512MB each) on same disk (file1, file2) and
> +  launch two dd threads in different cgroup to read those files.
> +
> +	sync
> +	echo 3 > /proc/sys/vm/drop_caches
> +
> +	dd if=/mnt/sdb/zerofile1 of=/dev/null &
> +	echo $! > /cgroup/test1/tasks
> +	cat /cgroup/test1/tasks
> +
> +	dd if=/mnt/sdb/zerofile2 of=/dev/null &
> +	echo $! > /cgroup/test2/tasks
> +	cat /cgroup/test2/tasks
> +
> +- At macro level, first dd should finish first. To get more precise data, keep
> +  on looking at (with the help of script), at blkio.disk_time and
> +  blkio.disk_sectors files of both test1 and test2 groups. This will tell how
> +  much disk time (in milli seconds), each group got and how many secotors each
> +  group dispatched to the disk. We provide fairness in terms of disk time, so
> +  ideally io.disk_time of cgroups should be in proportion to the weight.
> +
> +Various user visible config options
> +===================================
> +CONFIG_CFQ_GROUP_IOSCHED
> +	- Enables group scheduling in CFQ. Currently only 1 level of group
> +	  creation is allowed.
> +
> +CONFIG_DEBUG_CFQ_IOSCHED
> +	- Enables some debugging messages in blktrace. Also creates extra
> +	  cgroup file blkio.dequeue.
> +
> +Config options selected automatically
> +=====================================
> +These config options are not user visible and are selected/deselected
> +automatically based on IO scheduler configuration.
> +
> +CONFIG_BLK_CGROUP
> +	- Block IO controller. Selected by CONFIG_CFQ_GROUP_IOSCHED.
> +
> +CONFIG_DEBUG_BLK_CGROUP
> +	- Debug help. Selected by CONFIG_DEBUG_CFQ_IOSCHED.
> +
> +Details of cgroup files
> +=======================
> +- blkio.ioprio_class
> +	- Specifies class of the cgroup (RT, BE, IDLE). This is default io
> +	  class of the group on all the devices.
> +
> +	  1 = RT; 2 = BE, 3 = IDLE
> +
> +- blkio.weight
> +	- Specifies per cgroup weight.
> +
> +	  Currently allowed range of weights is from 100 to 1000.
> +
> +- blkio.time
> +	- disk time allocated to cgroup per device in milliseconds. First
> +	  two fields specify the major and minor number of the device and
> +	  third field specifies the disk time allocated to group in
> +	  milliseconds.
> +
> +- blkio.sectors
> +	- number of sectors transferred to/from disk by the group. First
> +	  two fields specify the major and minor number of the device and
> +	  third field specifies the number of sectors transferred by the
> +	  group to/from the device.
> +
> +- blkio.dequeue
> +	- Debugging aid only enabled if CONFIG_DEBUG_CFQ_IOSCHED=y. This
> +	  gives the statistics about how many a times a group was dequeued
> +	  from service tree of the device. First two fields specify the major
> +	  and minor number of the device and third field specifies the number
> +	  of times a group was dequeued from a particular device.

Hi, Vivek,

Are the parameters inter-related? What if you have conflicts w.r.t.
time, sectors, etc?

-- 
	Balbir
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