Messages in this thread | | | Date | Thu, 28 Oct 2021 10:08:02 +0800 | Subject | Re: [RFC PATCH] sched/fair: use max_spare_cap_cpu if it is more energy efficient | From | brookxu <> |
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Dietmar Eggemann wrote on 2021/10/25 9:04 下午: > On 22/10/2021 06:05, Xuewen Yan wrote: >> Hi Chunguang >> >> brookxu <brookxu.cn@gmail.com> 于2021年10月21日周四 下午4:24写道: >>> >>> From: Chunguang Xu <brookxu@tencent.com> >>> >>> When debugging EAS, I found that if the task is migrated to >>> max_spare_cap_cpu, even if the power consumption of pd is lower, > > The task p hasn't been migrated yet. `max_spare_cap_cpu` here is only a > potential candidate CPU to be selected for p. > >>> we still put the task on prev_cpu. Maybe we should fix it. >>> >>> Signed-off-by: Chunguang Xu <brookxu@tencent.com> >>> --- >>> kernel/sched/fair.c | 4 +++- >>> 1 file changed, 3 insertions(+), 1 deletion(-) >>> >>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c >>> index ff69f245b939..2ae7e03de6d2 100644 >>> --- a/kernel/sched/fair.c >>> +++ b/kernel/sched/fair.c >>> @@ -6867,8 +6867,10 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu) >>> /* Evaluate the energy impact of using max_spare_cap_cpu. */ >>> if (max_spare_cap_cpu >= 0) { >>> cur_delta = compute_energy(p, max_spare_cap_cpu, pd); >>> - if (cur_delta < base_energy_pd) >> >> this is aimed to prevent the cur_delta < 0, and usuallly, when the >> task was put on the max_spare_cpu, the cur_power should be bigger than >> base_pd_power, >> if the cur_power < base_pd_power, the cpu util may have changed, at >> this time, we should keep prev_cpu. >> >> You can look at below discuss and patch: >> https://lore.kernel.org/all/20210429101948.31224-3-Pierre.Gondois@arm.com/ >> https://lore.kernel.org/all/CAB8ipk_vgtg5d1obH36BYfNLZosbwr2k_U3xnAD4=H5uZt_M_g@mail.gmail.com/ > > That's correct. `prev_delta < base_energy_pd` or `cur_delta < > base_energy_pd` indicate the rare case that `compute_energy() { -> > cpu_util_next() -> cpu util }` returns a higher energy value for the > perf domain w/o the task p than w/ it. > > `base_energy_pd` stands for the energy spend on the CPUs of the Perf > Domain (PD) w/o considering the task p (compute_energy(p, *-1*, pd)), > `dst_cpu == -1`. > > If this happens to a candidate CPU (prev_cpu or a per-PD > max_spare_cap_cpu) we bail out and return target (i.e. prev_cpu) because > we can't compare the energy values (prev_delta and best_delta) later on > in this case.
Right, thanks all :)
> [...] >
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