Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/dtor/input

[pandora-kernel.git] / Documentation / sched-design-CFS.txt

diff --git a/Documentation/sched-design-CFS.txt b/Documentation/sched-design-CFS.txt
index 16feebb..88bcb87 100644 (file)
--- a/Documentation/sched-design-CFS.txt
+++ b/Documentation/sched-design-CFS.txt
@@ -83,7 +83,7 @@ Some implementation details:
    CFS uses nanosecond granularity accounting and does not rely on any
    jiffies or other HZ detail. Thus the CFS scheduler has no notion of
    'timeslices' and has no heuristics whatsoever. There is only one
-   central tunable:
+   central tunable (you have to switch on CONFIG_SCHED_DEBUG):
 
          /proc/sys/kernel/sched_granularity_ns
 
@@ -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