Messages in this thread | | | Date | Mon, 15 Aug 2022 10:54:56 +0800 | Subject | Re: [PATCH 1/5] sched/fair: ignore SIS_UTIL when has idle core | From | Abel Wu <> |
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On 8/4/22 5:59 PM, Chen Yu Wrote: > On Thu, Jul 14, 2022 at 3:11 PM Abel Wu <wuyun.abel@bytedance.com> 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? >> > I took a look at this patch again before I start a OLTP test. I > thought the position change of > dereference sd_llc might not be closely connected with current change > as Yicong mentioned.
OK, I will make it a separate patch. But before that I'd prefer wait for more comments :)
> Besides, after moving the dereference inside SIS_PROP, we might do > cpumask_and() no matter whether > sd_llc is valid or not, which might be of extra cost? > I think it might be irrelevant whether the local sd_llc is valid or not, since all we care about is target sd_llc if !SIS_PROP.
Best Regards, Abel
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