Messages in this thread | | | Subject | Re: [PATCH 1/5] sched/fair: ignore SIS_UTIL when has idle core | From | Yicong Yang <> | Date | Thu, 14 Jul 2022 15:15:04 +0800 |
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On 2022/7/14 14:58, Abel Wu wrote: > > 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? >
It just makes me think that dereference is unnecessary if this_cpu and target locates in the same LLC, since it's already been passed. But since you noticed no difference it may have little effect. :)
> 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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