aboutsummaryrefslogtreecommitdiffstats
path: root/Documentation
diff options
context:
space:
mode:
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/scheduler/sched-design-CFS.txt54
-rw-r--r--Documentation/scheduler/sched-rt-group.txt20
2 files changed, 7 insertions, 67 deletions
diff --git a/Documentation/scheduler/sched-design-CFS.txt b/Documentation/scheduler/sched-design-CFS.txt
index 6f33593e59e2..8239ebbcddce 100644
--- a/Documentation/scheduler/sched-design-CFS.txt
+++ b/Documentation/scheduler/sched-design-CFS.txt
@@ -211,7 +211,7 @@ provide fair CPU time to each such task group. For example, it may be
211desirable to first provide fair CPU time to each user on the system and then to 211desirable to first provide fair CPU time to each user on the system and then to
212each task belonging to a user. 212each task belonging to a user.
213 213
214CONFIG_GROUP_SCHED strives to achieve exactly that. It lets tasks to be 214CONFIG_CGROUP_SCHED strives to achieve exactly that. It lets tasks to be
215grouped and divides CPU time fairly among such groups. 215grouped and divides CPU time fairly among such groups.
216 216
217CONFIG_RT_GROUP_SCHED permits to group real-time (i.e., SCHED_FIFO and 217CONFIG_RT_GROUP_SCHED permits to group real-time (i.e., SCHED_FIFO and
@@ -220,38 +220,11 @@ SCHED_RR) tasks.
220CONFIG_FAIR_GROUP_SCHED permits to group CFS (i.e., SCHED_NORMAL and 220CONFIG_FAIR_GROUP_SCHED permits to group CFS (i.e., SCHED_NORMAL and
221SCHED_BATCH) tasks. 221SCHED_BATCH) tasks.
222 222
223At present, there are two (mutually exclusive) mechanisms to group tasks for 223 These options need CONFIG_CGROUPS to be defined, and let the administrator
224CPU bandwidth control purposes:
225
226 - Based on user id (CONFIG_USER_SCHED)
227
228 With this option, tasks are grouped according to their user id.
229
230 - Based on "cgroup" pseudo filesystem (CONFIG_CGROUP_SCHED)
231
232 This options needs CONFIG_CGROUPS to be defined, and lets the administrator
233 create arbitrary groups of tasks, using the "cgroup" pseudo filesystem. See 224 create arbitrary groups of tasks, using the "cgroup" pseudo filesystem. See
234 Documentation/cgroups/cgroups.txt for more information about this filesystem. 225 Documentation/cgroups/cgroups.txt for more information about this filesystem.
235 226
236Only one of these options to group tasks can be chosen and not both. 227When CONFIG_FAIR_GROUP_SCHED is defined, a "cpu.shares" file is created for each
237
238When CONFIG_USER_SCHED is defined, a directory is created in sysfs for each new
239user and a "cpu_share" file is added in that directory.
240
241 # cd /sys/kernel/uids
242 # cat 512/cpu_share # Display user 512's CPU share
243 1024
244 # echo 2048 > 512/cpu_share # Modify user 512's CPU share
245 # cat 512/cpu_share # Display user 512's CPU share
246 2048
247 #
248
249CPU bandwidth between two users is divided in the ratio of their CPU shares.
250For example: if you would like user "root" to get twice the bandwidth of user
251"guest," then set the cpu_share for both the users such that "root"'s cpu_share
252is twice "guest"'s cpu_share.
253
254When CONFIG_CGROUP_SCHED is defined, a "cpu.shares" file is created for each
255group created using the pseudo filesystem. See example steps below to create 228group created using the pseudo filesystem. See example steps below to create
256task groups and modify their CPU share using the "cgroups" pseudo filesystem. 229task groups and modify their CPU share using the "cgroups" pseudo filesystem.
257 230
@@ -273,24 +246,3 @@ task groups and modify their CPU share using the "cgroups" pseudo filesystem.
273 246
274 # #Launch gmplayer (or your favourite movie player) 247 # #Launch gmplayer (or your favourite movie player)
275 # echo <movie_player_pid> > multimedia/tasks 248 # echo <movie_player_pid> > multimedia/tasks
276
2778. Implementation note: user namespaces
278
279User namespaces are intended to be hierarchical. But they are currently
280only partially implemented. Each of those has ramifications for CFS.
281
282First, since user namespaces are hierarchical, the /sys/kernel/uids
283presentation is inadequate. Eventually we will likely want to use sysfs
284tagging to provide private views of /sys/kernel/uids within each user
285namespace.
286
287Second, the hierarchical nature is intended to support completely
288unprivileged use of user namespaces. So if using user groups, then
289we want the users in a user namespace to be children of the user
290who created it.
291
292That is currently unimplemented. So instead, every user in a new
293user namespace will receive 1024 shares just like any user in the
294initial user namespace. Note that at the moment creation of a new
295user namespace requires each of CAP_SYS_ADMIN, CAP_SETUID, and
296CAP_SETGID.
diff --git a/Documentation/scheduler/sched-rt-group.txt b/Documentation/scheduler/sched-rt-group.txt
index 86eabe6c3419..605b0d40329d 100644
--- a/Documentation/scheduler/sched-rt-group.txt
+++ b/Documentation/scheduler/sched-rt-group.txt
@@ -126,23 +126,12 @@ priority!
1262.3 Basis for grouping tasks 1262.3 Basis for grouping tasks
127---------------------------- 127----------------------------
128 128
129There are two compile-time settings for allocating CPU bandwidth. These are 129Enabling CONFIG_RT_GROUP_SCHED lets you explicitly allocate real
130configured using the "Basis for grouping tasks" multiple choice menu under 130CPU bandwidth to task groups.
131General setup > Group CPU Scheduler:
132
133a. CONFIG_USER_SCHED (aka "Basis for grouping tasks" = "user id")
134
135This lets you use the virtual files under
136"/sys/kernel/uids/<uid>/cpu_rt_runtime_us" to control he CPU time reserved for
137each user .
138
139The other option is:
140
141.o CONFIG_CGROUP_SCHED (aka "Basis for grouping tasks" = "Control groups")
142 131
143This uses the /cgroup virtual file system and 132This uses the /cgroup virtual file system and
144"/cgroup/<cgroup>/cpu.rt_runtime_us" to control the CPU time reserved for each 133"/cgroup/<cgroup>/cpu.rt_runtime_us" to control the CPU time reserved for each
145control group instead. 134control group.
146 135
147For more information on working with control groups, you should read 136For more information on working with control groups, you should read
148Documentation/cgroups/cgroups.txt as well. 137Documentation/cgroups/cgroups.txt as well.
@@ -161,8 +150,7 @@ For now, this can be simplified to just the following (but see Future plans):
161=============== 150===============
162 151
163There is work in progress to make the scheduling period for each group 152There is work in progress to make the scheduling period for each group
164("/sys/kernel/uids/<uid>/cpu_rt_period_us" or 153("/cgroup/<cgroup>/cpu.rt_period_us") configurable as well.
165"/cgroup/<cgroup>/cpu.rt_period_us" respectively) configurable as well.
166 154
167The constraint on the period is that a subgroup must have a smaller or 155The constraint on the period is that a subgroup must have a smaller or
168equal period to its parent. But realistically its not very useful _yet_ 156equal period to its parent. But realistically its not very useful _yet_