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SubjectRe: [RFC PATCH v2 00/17] Core scheduling v2
Date
> Thanks for pointing this out. I think the ideal fix would be to
> correctly initialize/cleanup the coresched attributes in the cpu
> hotplug code path so that lock could be taken successfully if the
> sibling is offlined/onlined after coresched was enabled. We are
> working on another bug related to hotplugpath and shall introduce
> the fix in v3.
>
A possible fix for handling the runqueues during cpu offline/online
is attached here with.

Thanks,
Vineeth

---
kernel/sched/core.c | 28 +++++++++++++++++++++++++---
1 file changed, 25 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index e8e5f26db052..1a809849a1e7 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -253,7 +253,7 @@ static int __sched_core_stopper(void *data)
bool enabled = !!(unsigned long)data;
int cpu;

- for_each_possible_cpu(cpu)
+ for_each_online_cpu(cpu)
cpu_rq(cpu)->core_enabled = enabled;

return 0;
@@ -3764,6 +3764,9 @@ pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
struct rq *rq_i = cpu_rq(i);
struct task_struct *p;

+ if (cpu_is_offline(i))
+ continue;
+
if (rq_i->core_pick)
continue;

@@ -3866,6 +3869,9 @@ next_class:;
for_each_cpu(i, smt_mask) {
struct rq *rq_i = cpu_rq(i);

+ if (cpu_is_offline(i))
+ continue;
+
WARN_ON_ONCE(!rq_i->core_pick);

rq_i->core_pick->core_occupation = occ;
@@ -6410,8 +6416,14 @@ int sched_cpu_activate(unsigned int cpu)
/*
* When going up, increment the number of cores with SMT present.
*/
- if (cpumask_weight(cpu_smt_mask(cpu)) == 2)
+ if (cpumask_weight(cpu_smt_mask(cpu)) == 2) {
static_branch_inc_cpuslocked(&sched_smt_present);
+#ifdef CONFIG_SCHED_CORE
+ if (static_branch_unlikely(&__sched_core_enabled)) {
+ rq->core_enabled = true;
+ }
+#endif
+ }
#endif
set_cpu_active(cpu, true);

@@ -6459,8 +6471,15 @@ int sched_cpu_deactivate(unsigned int cpu)
/*
* When going down, decrement the number of cores with SMT present.
*/
- if (cpumask_weight(cpu_smt_mask(cpu)) == 2)
+ if (cpumask_weight(cpu_smt_mask(cpu)) == 2) {
+#ifdef CONFIG_SCHED_CORE
+ struct rq *rq = cpu_rq(cpu);
+ if (static_branch_unlikely(&__sched_core_enabled)) {
+ rq->core_enabled = false;
+ }
+#endif
static_branch_dec_cpuslocked(&sched_smt_present);
+ }
#endif

if (!sched_smp_initialized)
@@ -6537,6 +6556,9 @@ int sched_cpu_dying(unsigned int cpu)
update_max_interval();
nohz_balance_exit_idle(rq);
hrtick_clear(rq);
+#ifdef CONFIG_SCHED_CORE
+ rq->core = NULL;
+#endif
return 0;
}
#endif
--
2.17.1
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