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    SubjectRe: [PATCH 1/5] sched/fair: ignore SIS_UTIL when has idle core
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    On 7/14/22 2:19 PM, Yicong Yang Wrote:
    > On 2022/7/12 16:20, Abel Wu wrote:
    >> When SIS_UTIL is enabled, SIS domain scan will be skipped if
    >> the LLC is overloaded. Since the overloaded status is checked
    >> in the load balancing at LLC level, the interval is llc_size
    >> miliseconds. The duration might be long enough to affect the
    >> overall system throughput if idle cores are out of reach in
    >> SIS domain scan.
    >>
    >> Signed-off-by: Abel Wu <wuyun.abel@bytedance.com>
    >> ---
    >> kernel/sched/fair.c | 15 +++++++++------
    >> 1 file changed, 9 insertions(+), 6 deletions(-)
    >>
    >> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
    >> index a78d2e3b9d49..cd758b3616bd 100644
    >> --- a/kernel/sched/fair.c
    >> +++ b/kernel/sched/fair.c
    >> @@ -6392,16 +6392,19 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, bool
    >> struct sched_domain *this_sd;
    >> u64 time = 0;
    >>
    >> - this_sd = rcu_dereference(*this_cpu_ptr(&sd_llc));
    >> - if (!this_sd)
    >> - return -1;
    >> -
    >> cpumask_and(cpus, sched_domain_span(sd), p->cpus_ptr);
    >>
    >> - if (sched_feat(SIS_PROP) && !has_idle_core) {
    >> + if (has_idle_core)
    >> + goto scan;
    >> +
    >> + if (sched_feat(SIS_PROP)) {
    >> u64 avg_cost, avg_idle, span_avg;
    >> unsigned long now = jiffies;
    >>
    >> + this_sd = rcu_dereference(*this_cpu_ptr(&sd_llc));
    >> + if (!this_sd)
    >> + return -1;
    >> +
    >
    > I don't follow the change here. True that this_sd is used only in SIS_PROP, but it seems irrelevant with your
    > commit. Does the position of this make any performance difference?

    No, this change doesn't make much difference to performance. Are
    you suggesting that I should make this a separate patch?

    Thanks,
    Abel

    >
    > Thanks.
    >
    >> /*
    >> * If we're busy, the assumption that the last idle period
    >> * predicts the future is flawed; age away the remaining
    >> @@ -6436,7 +6439,7 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, bool
    >> return -1;
    >> }
    >> }
    >> -
    >> +scan:
    >> for_each_cpu_wrap(cpu, cpus, target + 1) {
    >> if (has_idle_core) {
    >> i = select_idle_core(p, cpu, cpus, &idle_cpu);
    >>

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