@@ -447,6 +447,85 @@ static void free_trial_cpuset(struct cpuset *trial)
kfree(trial);
}
+static bool cpuset_has_dl_tasks(struct cpuset *cs)
+{
+ bool dl_tasks = false;
+ struct css_task_iter it;
+ struct task_struct *task;
+
+ /* Go through each task in @cs looking for a DL task */
+ css_task_iter_start(&cs->css, &it);
+
+ while (!dl_tasks && (task = css_task_iter_next(&it))) {
+ if (dl_task(task))
+ dl_tasks = true;
+ }
+
+ css_task_iter_end(&it);
+
+ return dl_tasks;
+}
+
+/*
+ * Assumes RCU read lock and cpuset_mutex are held.
+ */
+static int validate_dl_change(struct cpuset *cur, struct cpuset *trial)
+{
+ bool populated = false, dl_tasks = false;
+ int ret = -EBUSY;
+ struct cgroup_subsys_state *pos_css;
+ struct cpuset *cs;
+
+ /*
+ * The cpuset.sched_load_balance flag is flipped off on
+ * the current cpuset.
+ */
+ if (is_sched_load_balance(cur) &&
+ !is_sched_load_balance(trial)) {
+ /* See if at least one descendant cpuset is populated */
+ cpuset_for_each_descendant_pre(cs, pos_css, cur) {
+ /* Skip over ourselve */
+ if (cs == cur)
+ continue;
+
+ /* Empty cpusets are of no interest */
+ if (cpumask_empty(cs->cpus_allowed)) {
+ pos_css = css_rightmost_descendant(pos_css);
+ continue;
+ }
+
+ /*
+ * @cur has at least one children and CPUs have been
+ * assigned to it - there is no need to go further.
+ */
+ populated = true;
+ break;
+ }
+
+ dl_tasks = cpuset_has_dl_tasks(cur);
+
+ /*
+ * This CPUset has a children that is populated by (at least)
+ * one CPU. When the sched_load_balance flag gets flipped off
+ * it will create a new root domain for the children CPUset,
+ * and that new root domain will include the CPUs assigned to
+ * the CPUset.
+ *
+ * Since the tasks in the current CPUset have not been assigned
+ * to the children CPUset they will simply stay here and use
+ * all the CPUs available in this set. For DL tasks this can't
+ * be allowed since they will be executing on CPUs associated to
+ * more than one root domains.
+ */
+ if (populated && dl_tasks)
+ goto out;
+ }
+
+ ret = 0;
+out:
+ return ret;
+}
+
/*
* validate_change() - Used to validate that any proposed cpuset change
* follows the structural rules for cpusets.
@@ -481,6 +560,9 @@ static int validate_change(struct cpuset *cur, struct cpuset *trial)
if (!is_cpuset_subset(c, trial))
goto out;
+ if (validate_dl_change(cur, trial))
+ goto out;
+
/* Remaining checks don't apply to root cpuset */
ret = 0;
if (cur == &top_cpuset)
This patch prevents the 'sched_load_balance' flag from being fippled off when DL tasks are present in a CPUset. Otherwise we end up with the DL tasks using CPUs belonging to different root domains, something that breaks the mathematical model behind DL bandwidth management. For example on a 4 core system CPUset "set1" has been created and CPUs 0 and 1 assigned to it. A DL task has also been spun off. By default the DL task can use all the CPUs in the default CPUset. If we set the base CPUset's cpuset.sched_load_balance to '0', CPU 0 and 1 are added to a newly created root domain while CPU 2 and 3 endup in the default root domain. But the DL task is still part of the base CPUset and as such can use CPUs 0 to 3, spanning at the same time more than one root domain. Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org> --- kernel/cgroup/cpuset.c | 82 ++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 82 insertions(+) -- 2.7.4