On 18/02/2025 06:44, Shrikanth Hegde wrote:
[...]
@@ -1352,6 +1352,9 @@ bool sched_can_stop_tick(struct rq *rq)
if (rq->cfs.h_nr_queued > 1)
return false;
+ if (rq->cfs.nr_running > 0 && arch_cpu_parked(cpu_of(rq)))
+ return false;
+
you mean rq->cfs.h_nr_queued or rq->nr_running ?
cfs.h_nr_queued is probably more sensible, will use that.
[...]
@@ -11259,6 +11293,8 @@ static inline void calculate_imbalance(struct
lb_env *env, struct sd_lb_stats *s
* avg_load : Only if imbalance is significant enough.
* nr_idle : dst_cpu is not busy and the number of idle CPUs is quite
* different in groups.
+ * nr_task : balancing can go either way depending on the number of
running tasks
+ * per group
*/
This comment on nr_task can be removed as it is not present in the list.
Consider it gone.
[...]
@@ -11766,7 +11822,7 @@ static int sched_balance_rq(int this_cpu,
struct rq *this_rq,
ld_moved = 0;
/* Clear this flag as soon as we find a pullable task */
env.flags |= LBF_ALL_PINNED;
- if (busiest->nr_running > 1) {
+ if (busiest->nr_running > 1 || arch_cpu_parked(busiest->cpu)) {
Since there is reliance on active balance if there is single task, it
think above isn't needed. Is there any usecase for it?
Seems to work without that check. I have no particular use case in mind.
/*
* Attempt to move tasks. If sched_balance_find_src_group
has found
* an imbalance but busiest->nr_running <= 1, the group is
@@ -12356,6 +12412,11 @@ static void nohz_balancer_kick(struct rq *rq)
if (time_before(now, nohz.next_balance))
goto out;
+ if (!idle_cpu(rq->cpu)) {
+ flags = NOHZ_STATS_KICK | NOHZ_BALANCE_KICK;
+ goto out;
+ }
+
This could be agrressive. Note when the code comes here, it is not idle.
It would bail out early if it is idle.
It seems like we can do without this one as well.
if (rq->nr_running >= 2) {
flags = NOHZ_STATS_KICK | NOHZ_BALANCE_KICK;
goto out;
@@ -12767,6 +12828,9 @@ static int sched_balance_newidle(struct rq
*this_rq, struct rq_flags *rf)
update_misfit_status(NULL, this_rq);
+ if (arch_cpu_parked(this_cpu))
+ return 0;
+
/*
* There is a task waiting to run. No need to search for one.
* Return 0; the task will be enqueued when switching to idle.
diff --git a/kernel/sched/syscalls.c b/kernel/sched/syscalls.c
index 456d339be98f..7efd76a30be7 100644
--- a/kernel/sched/syscalls.c
+++ b/kernel/sched/syscalls.c
@@ -214,6 +214,9 @@ int idle_cpu(int cpu)
return 0;
#endif
+ if (arch_cpu_parked(cpu))
+ return 0;
+
return 1;
}
