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SubjectRe: [PATCH 01/20] blkio: Documentation
* Vivek Goyal <vgoyal@redhat.com> [2009-11-03 18:43:38]:

> Signed-off-by: Vivek Goyal <vgoyal@redhat.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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