[PATCH v7 2/5] cpuset: Add cpuset.sched_load_balance to v2

Waiman Long
2018-04-19T13:47:19Z

The sched_load_balance flag is needed to enable CPU isolation similar
to what can be done with the "isolcpus" kernel boot parameter.

The sched_load_balance flag implies an implicit !cpu_exclusive as
it doesn't make sense to have an isolated CPU being load-balanced in
another cpuset.

For v2, this flag is hierarchical and is inherited by child cpusets. It
is not allowed to have this flag turn off in a parent cpuset, but on
in a child cpuset.

This flag is set by the parent and is not delegatable.

Signed-off-by: Waiman Long <longman@redhat.com>
---
Documentation/cgroup-v2.txt | 22 ++++++++++++++++++
kernel/cgroup/cpuset.c | 56 +++++++++++++++++++++++++++++++++++++++------
2 files changed, 71 insertions(+), 7 deletions(-)

diff --git a/Documentation/cgroup-v2.txt b/Documentation/cgroup-v2.txt
index ed8ec66..c970bd7 100644
--- a/Documentation/cgroup-v2.txt
+++ b/Documentation/cgroup-v2.txt
@@ -1514,6 +1514,28 @@ Cpuset Interface Files
it is a subset of "cpuset.mems". Its value will be affected
by memory nodes hotplug events.

+ cpuset.sched_load_balance
+ A read-write single value file which exists on non-root cgroups.
+ The default is "1" (on), and the other possible value is "0"
+ (off).
+
+ When it is on, tasks within this cpuset will be load-balanced
+ by the kernel scheduler. Tasks will be moved from CPUs with
+ high load to other CPUs within the same cpuset with less load
+ periodically.
+
+ When it is off, there will be no load balancing among CPUs on
+ this cgroup. Tasks will stay in the CPUs they are running on
+ and will not be moved to other CPUs.
+
+ This flag is hierarchical and is inherited by child cpusets. It
+ can be turned off only when the CPUs in this cpuset aren't
+ listed in the cpuset.cpus of other sibling cgroups, and all
+ the child cpusets, if present, have this flag turned off.
+
+ Once it is off, it cannot be turned back on as long as the
+ parent cgroup still has this flag in the off state.
+

Device controller
-----------------
diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 419b758..50c9254 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -407,15 +407,22 @@ static void cpuset_update_task_spread_flag(struct cpuset *cs,
*
* One cpuset is a subset of another if all its allowed CPUs and
* Memory Nodes are a subset of the other, and its exclusive flags
- * are only set if the other's are set. Call holding cpuset_mutex.
+ * are only set if the other's are set (on legacy hierarchy) or
+ * its sched_load_balance flag is only set if the other is set
+ * (on default hierarchy). Caller holding cpuset_mutex.
*/

static int is_cpuset_subset(const struct cpuset *p, const struct cpuset *q)
{
- return cpumask_subset(p->cpus_allowed, q->cpus_allowed) &&
- nodes_subset(p->mems_allowed, q->mems_allowed) &&
- is_cpu_exclusive(p) <= is_cpu_exclusive(q) &&
- is_mem_exclusive(p) <= is_mem_exclusive(q);
+ if (!cpumask_subset(p->cpus_allowed, q->cpus_allowed) ||
+ !nodes_subset(p->mems_allowed, q->mems_allowed))
+ return false;
+
+ if (cgroup_subsys_on_dfl(cpuset_cgrp_subsys))
+ return is_sched_load_balance(p) <= is_sched_load_balance(q);
+ else
+ return is_cpu_exclusive(p) <= is_cpu_exclusive(q) &&
+ is_mem_exclusive(p) <= is_mem_exclusive(q);
}

/**
@@ -498,7 +505,7 @@ static int validate_change(struct cpuset *cur, struct cpuset *trial)

par = parent_cs(cur);

- /* On legacy hiearchy, we must be a subset of our parent cpuset. */
+ /* On legacy hierarchy, we must be a subset of our parent cpuset. */
ret = -EACCES;
if (!is_in_v2_mode() && !is_cpuset_subset(trial, par))
goto out;
@@ -1327,6 +1334,19 @@ static int update_flag(cpuset_flagbits_t bit, struct cpuset *cs,
else
clear_bit(bit, &trialcs->flags);

+ /*
+ * On default hierarchy, turning off sched_load_balance flag implies
+ * an implicit cpu_exclusive. Turning on sched_load_balance will
+ * clear the cpu_exclusive flag.
+ */
+ if ((bit == CS_SCHED_LOAD_BALANCE) &&
+ cgroup_subsys_on_dfl(cpuset_cgrp_subsys)) {
+ if (turning_on)
+ clear_bit(CS_CPU_EXCLUSIVE, &trialcs->flags);
+ else
+ set_bit(CS_CPU_EXCLUSIVE, &trialcs->flags);
+ }
+
err = validate_change(cs, trialcs);
if (err < 0)
goto out;
@@ -1966,6 +1986,14 @@ static s64 cpuset_read_s64(struct cgroup_subsys_state *css, struct cftype *cft)
.flags = CFTYPE_NOT_ON_ROOT,
},

+ {
+ .name = "sched_load_balance",
+ .read_u64 = cpuset_read_u64,
+ .write_u64 = cpuset_write_u64,
+ .private = FILE_SCHED_LOAD_BALANCE,
+ .flags = CFTYPE_NOT_ON_ROOT,
+ },
+
{ } /* terminate */
};

@@ -1991,7 +2019,21 @@ static s64 cpuset_read_s64(struct cgroup_subsys_state *css, struct cftype *cft)
if (!alloc_cpumask_var(&cs->effective_cpus, GFP_KERNEL))
goto free_cpus;

- set_bit(CS_SCHED_LOAD_BALANCE, &cs->flags);
+ /*
+ * On default hierarchy, inherit parent's CS_SCHED_LOAD_BALANCE and
+ * CS_CPU_EXCLUSIVE flag.
+ */
+ if (cgroup_subsys_on_dfl(cpuset_cgrp_subsys)) {
+ struct cpuset *parent = css_cs(parent_css);
+
+ if (test_bit(CS_SCHED_LOAD_BALANCE, &parent->flags))
+ set_bit(CS_SCHED_LOAD_BALANCE, &cs->flags);
+ else
+ set_bit(CS_CPU_EXCLUSIVE, &cs->flags);
+ } else {
+ set_bit(CS_SCHED_LOAD_BALANCE, &cs->flags);
+ }
+
cpumask_clear(cs->cpus_allowed);
nodes_clear(cs->mems_allowed);
cpumask_clear(cs->effective_cpus);
--
1.8.3.1