Hi everyone, I'm happy to announce that I've implemented a Block I/O bandwidth controller. The controller is designed to be of use in a cgroup or virtual machine environment. The current approach is that the controller is implemented as a device-mapper driver. What's dm-band all about? ======================== Dm-band is an I/O bandwidth controller implemented as a device-mapper driver. Several jobs using the same physical device have to share the bandwidth of the device. Dm-band gives bandwidth to each job according to its weight, which each job can set its own value to. At this time, a job is a group of processes with the same pid or pgrp or uid. There is also a plan to make it support cgroup. A job can also be a virtual machine such as KVM or Xen. +------+ +------+ +------+ +------+ +------+ +------+ |cgroup| |cgroup| | the | | pid | | pid | | the | jobs | A | | B | |others| | X | | Y | |others| +--|---+ +--|---+ +--|---+ +--|---+ +--|---+ +--|---+ +--V----+---V---+----V---+ +--V----+---V---+----V---+ | group | group | default| | group | group | default| band groups | | | group | | | | group | +-------+-------+--------+ +-------+-------+--------+ | band1 | | band2 | band devices +-----------|------------+ +-----------|------------+ +-----------V--------------+-------------V------------+ | | | | sdb1 | sdb2 | physical devices +--------------------------+--------------------------+ How dm-band works. ======================== Every band device has one band group, which by default is called the default group. Band devices can also have extra band groups in them. Each band group has a job to support and a weight. Proportional to the weight, dm-band gives tokens to the group. A group passes on I/O requests that its job issues to the underlying layer so long as it has tokens left, while requests are blocked if there aren't any tokens left in the group. One token is consumed each time the group passes on a request. Dm-band will refill groups with tokens once all of groups that have requests on a given physical device use up their tokens. With this approach, a job running on a band group with large weight is guaranteed to be able to issue a large number of I/O requests. Getting started ============= The following is a brief description how to control the I/O bandwidth of disks. In this description, we'll take one disk with two partitions as an example target. You can also check the manual at Document/device-mapper/band.txt of the linux kernel source tree for more information. Create and map band devices --------------------------- Create two band devices "band1" and "band2" and map them to "/dev/sda1" and "/dev/sda2" respectively. # echo "0 `blockdev --getsize /dev/sda1` band /dev/sda1 1" | dmsetup create band1 # echo "0 `blockdev --getsize /dev/sda2` band /dev/sda2 1" | dmsetup create band2 If the commands are successful then the device files "/dev/mapper/band1" and "/dev/mapper/band2" will have been created. Bandwidth control ---------------- In this example weights of 40 and 10 will be assigned to "band1" and "band2" respectively. This is done using the following commands: # dmsetup message band1 0 weight 40 # dmsetup message band2 0 weight 10 After these commands, "band1" can use 80% --- 40/(40+10)*100 --- of the bandwidth of the physical disk "/dev/sda" while "band2" can use 20%. Additional bandwidth control --------------------------- In this example two extra band groups are created on "band1". The first group consists of all the processes with user-id 1000 and the second group consists of all the processes with user-id 2000. Their weights are 30 and 20 respectively. Firstly the band group type of "band1" is set to "user". Then, the user-id 1000 and 2000 groups are attached to "band1". Finally, weights are assigned to the user-id 1000 and 2000 groups. # dmsetup message band1 0 type user # dmsetup message band1 0 attach 1000 # dmsetup message band1 0 attach 2000 # dmsetup message band1 0 weight 1000:30 # dmsetup message band1 0 weight 2000:20 Now the processes in the user-id 1000 group can use 30% --- 30/(30+20+40+10)*100 --- of the bandwidth of the physical disk. Band Device Band Group Weight band1 user id 1000 30 band1 user id 2000 20 band1 default group(the other users) 40 band2 default group 10 Remove band devices ------------------- Remove the band devices when no longer used. # dmsetup remove band1 # dmsetup remove band2 TODO ======================== - Cgroup support. - Control read and write requests separately. - Support WRITE_BARRIER. - Optimization. - More configuration tools. Or is the dmsetup command sufficient? - Other policies to schedule BIOs. Or is the weight policy sufficient? Thanks, Ryo Tsuruta -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
