[PATCH 2/4] sched/fair: Move avg_scan_cost calculations under SIS_PROP

[Li, Aubrey]

On 2020/12/9 0:03, Vincent Guittot wrote:
> On Tue, 8 Dec 2020 at 16:35, Mel Gorman <mgorman at techsingularity.net> wrote:
>>
>> As noted by Vincent Guittot, avg_scan_costs are calculated for SIS_PROP
>> even if SIS_PROP is disabled. Move the time calculations under a SIS_PROP
>> check and while we are at it, exclude the cost of initialising the CPU
>> mask from the average scan cost.
>>
>> Signed-off-by: Mel Gorman <mgorman at techsingularity.net>
>> ---
>>  kernel/sched/fair.c | 14 ++++++++------
>>  1 file changed, 8 insertions(+), 6 deletions(-)
>>
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index ac7b34e7372b..5c41875aec23 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -6153,6 +6153,8 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t
>>         if (!this_sd)
>>                 return -1;
> 
> Just noticed while reviewing the patch that the above related to
> this_sd can also go under sched_feat(SIS_PROP)
> 
>>
>> +       cpumask_and(cpus, sched_domain_span(sd), p->cpus_ptr);
>> +
>>         if (sched_feat(SIS_PROP)) {
>>                 u64 avg_cost, avg_idle, span_avg;
>>
>> @@ -6168,11 +6170,9 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t
>>                         nr = div_u64(span_avg, avg_cost);
>>                 else
>>                         nr = 4;
>> -       }
>> -
>> -       time = cpu_clock(this);
>>
>> -       cpumask_and(cpus, sched_domain_span(sd), p->cpus_ptr);
>> +               time = cpu_clock(this);
>> +       }
>>
>>         for_each_cpu_wrap(cpu, cpus, target) {
>>                 if (!--nr)

nr is the key of this throttling mechanism, need to be placed under sched_feat(SIS_PROP) as well.

Thanks,
-Aubrey