Hello Chenyu,
One question ...
On 9/11/2023 8:20 AM, Chen Yu wrote:
> [..snip..]
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index e20f50726ab8..fe3b760c9654 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> [..more snip..]
> @@ -7052,10 +7072,14 @@ static int select_idle_core(struct task_struct *p, int core, struct cpumask *cpu
> int cpu;
>
> for_each_cpu(cpu, cpu_smt_mask(core)) {
> - if (!available_idle_cpu(cpu)) {
> + bool cache_hot = sched_feat(SIS_CACHE) ?
> + sched_clock_cpu(cpu) < cpu_rq(cpu)->cache_hot_timeout : false;
> +
> + if (!available_idle_cpu(cpu) || cache_hot) {
> idle = false;
> if (*idle_cpu == -1) {
> - if (sched_idle_cpu(cpu) && cpumask_test_cpu(cpu, p->cpus_ptr)) {
> + if (sched_idle_cpu(cpu) && cpumask_test_cpu(cpu, p->cpus_ptr) &&
> + !cache_hot) {
Here, the CPU is running a SCHED_IDLE task ...
> *idle_cpu = cpu;
> break;
> }
... but just below this, there are following lines to cache the idle_cpu:
}
if (*idle_cpu == -1 && cpumask_test_cpu(cpu, p->cpus_ptr))
*idle_cpu = cpu;
Would it make sense to also add the same "cache_hot" check here when we
come across an idle CPU during the search for an idle core? Something
like:
- if (*idle_cpu == -1 && cpumask_test_cpu(cpu, p->cpus_ptr))
+ if (*idle_cpu == -1 && !cache_hot && cpumask_test_cpu(cpu, p->cpus_ptr))
*idle_cpu = cpu;
Implications with the above change:
If the entire core is idle, "select_idle_core()" will return the core
and the search will bail out in "select_idle_cpu()". Otherwise, the
cache-hot idle CPUs encountered during the search for idle core will be
ignored now and if "idle_cpu" is not -1, it contains an idle CPU that is
not cache-hot.
Thoughts?
> [..snip..]
--
Thanks and Regards,
Prateek