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| -rw-r--r-- | Documentation/sched-design-CFS.txt | 67 |
1 files changed, 67 insertions, 0 deletions
diff --git a/Documentation/sched-design-CFS.txt b/Documentation/sched-design-CFS.txt index 84901e7c0508..88bcb8767335 100644 --- a/Documentation/sched-design-CFS.txt +++ b/Documentation/sched-design-CFS.txt @@ -117,3 +117,70 @@ Some implementation details: iterators of the scheduling modules are used. The balancing code got quite a bit simpler as a result. + +Group scheduler extension to CFS +================================ + +Normally the scheduler operates on individual tasks and strives to provide +fair CPU time to each task. Sometimes, it may be desirable to group tasks +and provide fair CPU time to each such task group. For example, it may +be desirable to first provide fair CPU time to each user on the system +and then to each task belonging to a user. + +CONFIG_FAIR_GROUP_SCHED strives to achieve exactly that. It lets +SCHED_NORMAL/BATCH tasks be be grouped and divides CPU time fairly among such +groups. At present, there are two (mutually exclusive) mechanisms to group +tasks for CPU bandwidth control purpose: + + - Based on user id (CONFIG_FAIR_USER_SCHED) + In this option, tasks are grouped according to their user id. + - Based on "cgroup" pseudo filesystem (CONFIG_FAIR_CGROUP_SCHED) + This options lets the administrator create arbitrary groups + of tasks, using the "cgroup" pseudo filesystem. See + Documentation/cgroups.txt for more information about this + filesystem. + +Only one of these options to group tasks can be chosen and not both. + +Group scheduler tunables: + +When CONFIG_FAIR_USER_SCHED is defined, a directory is created in sysfs for +each new user and a "cpu_share" file is added in that directory. + + # cd /sys/kernel/uids + # cat 512/cpu_share # Display user 512's CPU share + 1024 + # echo 2048 > 512/cpu_share # Modify user 512's CPU share + # cat 512/cpu_share # Display user 512's CPU share + 2048 + # + +CPU bandwidth between two users are divided in the ratio of their CPU shares. +For ex: if you would like user "root" to get twice the bandwidth of user +"guest", then set the cpu_share for both the users such that "root"'s +cpu_share is twice "guest"'s cpu_share + + +When CONFIG_FAIR_CGROUP_SCHED is defined, a "cpu.shares" file is created +for each group created using the pseudo filesystem. See example steps +below to create task groups and modify their CPU share using the "cgroups" +pseudo filesystem + + # mkdir /dev/cpuctl + # mount -t cgroup -ocpu none /dev/cpuctl + # cd /dev/cpuctl + + # mkdir multimedia # create "multimedia" group of tasks + # mkdir browser # create "browser" group of tasks + + # #Configure the multimedia group to receive twice the CPU bandwidth + # #that of browser group + + # echo 2048 > multimedia/cpu.shares + # echo 1024 > browser/cpu.shares + + # firefox & # Launch firefox and move it to "browser" group + # echo <firefox_pid> > browser/tasks + + # #Launch gmplayer (or your favourite movie player) + # echo <movie_player_pid> > multimedia/tasks |