On 2020/12/8 23:34, Mel Gorman 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 <mgor...@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;
>
> + 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)
> return -1;
I thought about this again and here seems not to be consistent:
- even if nr reduces to 0, shouldn't avg_scan_cost be updated as well before
return -1?
- if avg_scan_cost is not updated because nr is throttled, the first
time = cpu_clock(this);
can be optimized. As nr is calculated and we already know which of the weight
of cpumask and nr is greater.
Thanks,
-Aubrey
