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Commit 734d4513 authored by Li Zefan's avatar Li Zefan Committed by Tejun Heo
Browse files

cpuset: update cs->effective_{cpus, mems} when config changes 



We're going to have separate user-configured masks and effective ones.

Eventually configured masks can only be changed by writing cpuset.cpus
and cpuset.mems, and they won't be restricted by parent cpuset. While
effective masks reflect cpu/memory hotplug and hierachical restriction,
and these are the real masks that apply to the tasks in the cpuset.

We calculate effective mask this way:
  - top cpuset's effective_mask == online_mask, otherwise
  - cpuset's effective_mask == configured_mask & parent effective_mask,
    if the result is empty, it inherits parent effective mask.

Those behavior changes are for default hierarchy only. For legacy
hierarchy, effective_mask and configured_mask are the same, so we won't
break old interfaces.

To make cs->effective_{cpus,mems} to be effective masks, we need to
  - update the effective masks at hotplug
  - update the effective masks at config change
  - take on ancestor's mask when the effective mask is empty

The second item is done here. We don't need to treat root_cs specially
in update_cpumasks_hier().

This won't introduce behavior change.

v3:
- add a WARN_ON() to check if effective masks are the same with configured
  masks on legacy hierarchy.
- pass trialcs->cpus_allowed to update_cpumasks_hier() and add a comment for
  it. Similar change for update_nodemasks_hier(). Suggested by Tejun.

v2:
- revise the comment in update_{cpu,node}masks_hier(), suggested by Tejun.
- fix to use @cp instead of @cs in these two functions.

Signed-off-by: default avatarLi Zefan <lizefan@huawei.com>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent 1344ab9c

kernel/cpuset.c

+54 −34
Original line number Diff line number Diff line
@@ -855,36 +855,45 @@ static void update_tasks_cpumask(struct cpuset *cs) 
}



/*

 * update_tasks_cpumask_hier - Update the cpumasks of tasks in the hierarchy.

 * @root_cs: the root cpuset of the hierarchy

 * @update_root: update root cpuset or not?

 * update_cpumasks_hier - Update effective cpumasks and tasks in the subtree

 * @cs: the cpuset to consider

 * @new_cpus: temp variable for calculating new effective_cpus

 *

 * When congifured cpumask is changed, the effective cpumasks of this cpuset

 * and all its descendants need to be updated.

 *

 * This will update cpumasks of tasks in @root_cs and all other empty cpusets

 * which take on cpumask of @root_cs.

 * On legacy hierachy, effective_cpus will be the same with cpu_allowed.

 *

 * Called with cpuset_mutex held

 */

static void update_tasks_cpumask_hier(struct cpuset *root_cs, bool update_root)

static void update_cpumasks_hier(struct cpuset *cs, struct cpumask *new_cpus)

{

	struct cpuset *cp;

	struct cgroup_subsys_state *pos_css;



	rcu_read_lock();

	cpuset_for_each_descendant_pre(cp, pos_css, root_cs) {

		if (cp == root_cs) {

			if (!update_root)

				continue;

		} else {

			/* skip the whole subtree if @cp have some CPU */

			if (!cpumask_empty(cp->cpus_allowed)) {

	cpuset_for_each_descendant_pre(cp, pos_css, cs) {

		struct cpuset *parent = parent_cs(cp);



		cpumask_and(new_cpus, cp->cpus_allowed, parent->effective_cpus);



		/* Skip the whole subtree if the cpumask remains the same. */

		if (cpumask_equal(new_cpus, cp->effective_cpus)) {

			pos_css = css_rightmost_descendant(pos_css);

			continue;

		}

		}



		if (!css_tryget_online(&cp->css))

			continue;

		rcu_read_unlock();



		mutex_lock(&callback_mutex);

		cpumask_copy(cp->effective_cpus, new_cpus);

		mutex_unlock(&callback_mutex);



		WARN_ON(!cgroup_on_dfl(cp->css.cgroup) &&

			!cpumask_equal(cp->cpus_allowed, cp->effective_cpus));



		update_tasks_cpumask(cp);



		rcu_read_lock();
@@ -940,7 +949,8 @@ static int update_cpumask(struct cpuset *cs, struct cpuset *trialcs, 
	cpumask_copy(cs->cpus_allowed, trialcs->cpus_allowed);

	mutex_unlock(&callback_mutex);



	update_tasks_cpumask_hier(cs, true);

	/* use trialcs->cpus_allowed as a temp variable */

	update_cpumasks_hier(cs, trialcs->cpus_allowed);



	if (is_load_balanced)

		rebuild_sched_domains_locked();
@@ -1091,36 +1101,45 @@ static void update_tasks_nodemask(struct cpuset *cs) 
}



/*

 * update_tasks_nodemask_hier - Update the nodemasks of tasks in the hierarchy.

 * @cs: the root cpuset of the hierarchy

 * @update_root: update the root cpuset or not?

 * update_nodemasks_hier - Update effective nodemasks and tasks in the subtree

 * @cs: the cpuset to consider

 * @new_mems: a temp variable for calculating new effective_mems

 *

 * When configured nodemask is changed, the effective nodemasks of this cpuset

 * and all its descendants need to be updated.

 *

 * This will update nodemasks of tasks in @root_cs and all other empty cpusets

 * which take on nodemask of @root_cs.

 * On legacy hiearchy, effective_mems will be the same with mems_allowed.

 *

 * Called with cpuset_mutex held

 */

static void update_tasks_nodemask_hier(struct cpuset *root_cs, bool update_root)

static void update_nodemasks_hier(struct cpuset *cs, nodemask_t *new_mems)

{

	struct cpuset *cp;

	struct cgroup_subsys_state *pos_css;



	rcu_read_lock();

	cpuset_for_each_descendant_pre(cp, pos_css, root_cs) {

		if (cp == root_cs) {

			if (!update_root)

				continue;

		} else {

			/* skip the whole subtree if @cp have some CPU */

			if (!nodes_empty(cp->mems_allowed)) {

	cpuset_for_each_descendant_pre(cp, pos_css, cs) {

		struct cpuset *parent = parent_cs(cp);



		nodes_and(*new_mems, cp->mems_allowed, parent->effective_mems);



		/* Skip the whole subtree if the nodemask remains the same. */

		if (nodes_equal(*new_mems, cp->effective_mems)) {

			pos_css = css_rightmost_descendant(pos_css);

			continue;

		}

		}



		if (!css_tryget_online(&cp->css))

			continue;

		rcu_read_unlock();



		mutex_lock(&callback_mutex);

		cp->effective_mems = *new_mems;

		mutex_unlock(&callback_mutex);



		WARN_ON(!cgroup_on_dfl(cp->css.cgroup) &&

			nodes_equal(cp->mems_allowed, cp->effective_mems));



		update_tasks_nodemask(cp);



		rcu_read_lock();
@@ -1188,7 +1207,8 @@ static int update_nodemask(struct cpuset *cs, struct cpuset *trialcs, 
	cs->mems_allowed = trialcs->mems_allowed;

	mutex_unlock(&callback_mutex);



	update_tasks_nodemask_hier(cs, true);

	/* use trialcs->mems_allowed as a temp variable */

	update_nodemasks_hier(cs, &cs->mems_allowed);

done:

	return retval;

}