Do not group pages by mobility type on low memory systems

[sfrench/cifs-2.6.git] / Documentation / sched-design-CFS.txt

diff --git a/Documentation/sched-design-CFS.txt b/Documentation/sched-design-CFS.txt
index 84901e7c05084e1f767d024b7f06cde1f19d6854..88bcb87673354302737be5bbaac5b8c049941d86 100644 (file)
--- 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