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Subject[PATCH v3 05/12] cpuset: use effective cpumask to build sched domains
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.

We should partition sched domains according to effective_cpus, which
is the real cpulist that takes effects on tasks in the cpuset.

This won't introduce behavior change.

v2:
- Add a comment for the call of rebuild_sched_domains(), suggested
by Tejun.

Signed-off-by: Li Zefan <lizefan@huawei.com>
---
kernel/cpuset.c | 28 +++++++++++++++++-----------
1 file changed, 17 insertions(+), 11 deletions(-)

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index f834002..60577cc 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -494,11 +494,11 @@ out:
#ifdef CONFIG_SMP
/*
* Helper routine for generate_sched_domains().
- * Do cpusets a, b have overlapping cpus_allowed masks?
+ * Do cpusets a, b have overlapping effective cpus_allowed masks?
*/
static int cpusets_overlap(struct cpuset *a, struct cpuset *b)
{
- return cpumask_intersects(a->cpus_allowed, b->cpus_allowed);
+ return cpumask_intersects(a->effective_cpus, b->effective_cpus);
}

static void
@@ -615,7 +615,7 @@ static int generate_sched_domains(cpumask_var_t **domains,
*dattr = SD_ATTR_INIT;
update_domain_attr_tree(dattr, &top_cpuset);
}
- cpumask_copy(doms[0], top_cpuset.cpus_allowed);
+ cpumask_copy(doms[0], top_cpuset.effective_cpus);

goto done;
}
@@ -719,7 +719,7 @@ restart:
struct cpuset *b = csa[j];

if (apn == b->pn) {
- cpumask_or(dp, dp, b->cpus_allowed);
+ cpumask_or(dp, dp, b->effective_cpus);
if (dattr)
update_domain_attr_tree(dattr + nslot, b);

@@ -771,7 +771,7 @@ static void rebuild_sched_domains_locked(void)
* passing doms with offlined cpu to partition_sched_domains().
* Anyways, hotplug work item will rebuild sched domains.
*/
- if (!cpumask_equal(top_cpuset.cpus_allowed, cpu_active_mask))
+ if (!cpumask_equal(top_cpuset.effective_cpus, cpu_active_mask))
goto out;

/* Generate domain masks and attrs */
@@ -870,6 +870,7 @@ static void update_cpumasks_hier(struct cpuset *cs, struct cpumask *new_cpus)
{
struct cpuset *cp;
struct cgroup_subsys_state *pos_css;
+ bool need_rebuild_sched_domains = false;

rcu_read_lock();
cpuset_for_each_descendant_pre(cp, pos_css, cs) {
@@ -903,10 +904,21 @@ static void update_cpumasks_hier(struct cpuset *cs, struct cpumask *new_cpus)

update_tasks_cpumask(cp);

+ /*
+ * If the effective cpumask of any non-empty cpuset is changed,
+ * we need to rebuild sched domains.
+ */
+ if (!cpumask_empty(cp->cpus_allowed) &&
+ is_sched_load_balance(cp))
+ need_rebuild_sched_domains = true;
+
rcu_read_lock();
css_put(&cp->css);
}
rcu_read_unlock();
+
+ if (need_rebuild_sched_domains)
+ rebuild_sched_domains_locked();
}

/**
@@ -919,7 +931,6 @@ static int update_cpumask(struct cpuset *cs, struct cpuset *trialcs,
const char *buf)
{
int retval;
- int is_load_balanced;

/* top_cpuset.cpus_allowed tracks cpu_online_mask; it's read-only */
if (cs == &top_cpuset)
@@ -950,17 +961,12 @@ static int update_cpumask(struct cpuset *cs, struct cpuset *trialcs,
if (retval < 0)
return retval;

- is_load_balanced = is_sched_load_balance(trialcs);
-
mutex_lock(&callback_mutex);
cpumask_copy(cs->cpus_allowed, trialcs->cpus_allowed);
mutex_unlock(&callback_mutex);

/* use trialcs->cpus_allowed as a temp variable */
update_cpumasks_hier(cs, trialcs->cpus_allowed);
-
- if (is_load_balanced)
- rebuild_sched_domains_locked();
return 0;
}

--
1.8.0.2


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