On 9/11/25 10:53 AM, K Prateek Nayak wrote:
Hello Shrikanth,
On 9/10/2025 11:12 PM, Shrikanth Hegde wrote:
@@ -8563,7 +8563,7 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu,
int wake_flags)
if (!is_rd_overutilized(this_rq()->rd)) {
new_cpu = find_energy_efficient_cpu(p, prev_cpu);
if (new_cpu >= 0)
- return new_cpu;
+ goto check_new_cpu;
Should this fallback to the overutilized path if the most energy
efficient CPU is found to be paravirtualized or should
find_energy_efficient_cpu() be made aware of it?
While thinking about this, are there any such system which has vCPUs and
overcommits and still has energy model backing it?
Highly unlikely. So, I am planning to put a warning there and see if any
such usage exists there.
new_cpu = prev_cpu;
}
@@ -8605,7 +8605,12 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int wake_flags)
}
rcu_read_unlock();
- return new_cpu;
+ /* If newly found or prev_cpu is a paravirt cpu, use current cpu */
+check_new_cpu:
+ if (is_cpu_paravirt(new_cpu))
+ return cpu;
+ else
nit. redundant else.
+ return new_cpu;
}
/*
@@ -11734,6 +11739,12 @@ static int sched_balance_rq(int this_cpu, struct rq
*this_rq,
cpumask_and(cpus, sched_domain_span(sd), cpu_active_mask);
+#ifdef CONFIG_PARAVIRT
+ /* Don't spread load to paravirt CPUs */
+ if (static_branch_unlikely(&cpu_paravirt_push_tasks))
+ cpumask_andnot(cpus, cpus, cpu_paravirt_mask);
+#endif
Can something similar be also be done in select_idle_sibling() and
sched_balance_find_dst_cpu() for wakeup path?
We have this pattern in select_task_rq_fair
cpu = smp_processor_id();
new_cpu = prev_cpu;
task is waking up after a while, so likely prev_cpu is marked as paravirt
and in such cases we should return current cpu. if current cpu is
paravirt(unlikely),
and prev_cpu is also paravirt, then should return current cpu.
In next sched tick it will be pushed out.
select_idle_sibling(p, prev_cpu, new_cpu); - (new_cpu will remain prev_cpu if
wake_affine doesn't change it)
Will have to change the prototype to send current cpu as well.
