Re: [PATCH] sched/fair: Use sched_energy_enabled()

[Dietmar Eggemann <dietmar.eggemann@arm.com>]

On 27.03.26 17:32, Vincent Guittot wrote:
> On Fri, 27 Mar 2026 at 17:18, K Prateek Nayak <kprateek.nayak@amd.com> wrote:
>>
>> Hello Vincent,
>>
>> On 3/27/2026 6:50 PM, Vincent Guittot wrote:
>>> Use helper sched_energy_enabled() everywhere we want to test if EAS is
>>> enabled instead of mixing sched_energy_enabled() and direct call to
>>> static_branch_unlikely().
>>>
>>> No functional change
>>>
>>> Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
>>
>> Feel free to include:
>>
>> Reviewed-by: K Prateek Nayak <kprateek.nayak@amd.com>
>> Tested-by: K Prateek Nayak <kprateek.nayak@amd.com>
>>
>>> ---
>>>  kernel/sched/topology.c | 9 ++++-----
>>>  1 file changed, 4 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
>>> index 43150591914b..5847b83d9d55 100644
>>> --- a/kernel/sched/topology.c
>>> +++ b/kernel/sched/topology.c
>>> @@ -273,7 +273,7 @@ void rebuild_sched_domains_energy(void)
>>>  static int sched_energy_aware_handler(const struct ctl_table *table, int write,
>>>               void *buffer, size_t *lenp, loff_t *ppos)
>>>  {
>>> -     int ret, state;
>>> +     int ret;
>>>
>>>       if (write && !capable(CAP_SYS_ADMIN))
>>>               return -EPERM;
>>> @@ -289,8 +289,7 @@ static int sched_energy_aware_handler(const struct ctl_table *table, int write,
>>>
>>>       ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
>>>       if (!ret && write) {
>>> -             state = static_branch_unlikely(&sched_energy_present);
>>> -             if (state != sysctl_sched_energy_aware)
>>> +             if (sysctl_sched_energy_aware != sched_energy_enabled())
>>
>> Quick tangential question:
>>
>> Since "sysctl_sched_energy_aware" is initialized to "1", if
>> build_perf_domains() returns false at boot, sysctl_sched_energy_aware
>> and sched_energy_enabled() will go out of sync and reading
>> "/proc/sys/kernel/sched_energy_aware" will still show "1" despite EAS
>> being disabled.
>>
>> Is that okay?
> 
> Isn't the call to sched_is_eas_possible() there to prevent this case ?

Yes, I think so:

 300 static const struct ctl_table sched_energy_aware_sysctls[] = {
 ...
 302                 .procname       = "sched_energy_aware",
 ...
 306                 .proc_handler   = sched_energy_aware_handler,

 273 sched_energy_aware_handler()

 ...
 281         if (!sched_is_eas_possible(cpu_active_mask)) { <-- !!!
 282                 if (write) {
 283                         return -EOPNOTSUPP;
 284                 } else {
 285                         *lenp = 0;
 286                         return 0;
 287                 }
 ...


# cat /proc/sys/kernel/sched_energy_aware
1

# ./set_cpufreq_ondemand.sh

cat /proc/sys/kernel/sched_energy_aware
[  391.591167] rd 0-5: Checking EAS: cpufreq is not ready


Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>

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