From: Chunguang Xu <[email protected]>
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,
we still put the task on prev_cpu. Maybe we should fix it.
Signed-off-by: Chunguang Xu <[email protected]>
---
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)
+ if (cur_delta < base_energy_pd) {
+ target = max_spare_cap_cpu;
goto unlock;
+ }
cur_delta -= base_energy_pd;
if (cur_delta < best_delta) {
best_delta = cur_delta;
--
2.30.0
Hi Chunguang
brookxu <[email protected]> 于2021年10月21日周四 下午4:24写道：
>
> From: Chunguang Xu <[email protected]>
>
> 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,
> we still put the task on prev_cpu. Maybe we should fix it.
>
> Signed-off-by: Chunguang Xu <[email protected]>
> ---
> 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/[email protected]/
https://lore.kernel.org/all/CAB8ipk_vgtg5d1obH36BYfNLZosbwr2k_U3xnAD4=H5uZt_M_g@mail.gmail.com/
> + if (cur_delta < base_energy_pd) {
> + target = max_spare_cap_cpu;
> goto unlock;
> + }
> cur_delta -= base_energy_pd;
> if (cur_delta < best_delta) {
> best_delta = cur_delta;
> --
> 2.30.0
>
On 22/10/2021 06:05, Xuewen Yan wrote:
> Hi Chunguang
>
> brookxu <[email protected]> 于2021年10月21日周四 下午4:24写道：
>>
>> From: Chunguang Xu <[email protected]>
>>
>> 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 <[email protected]>
>> ---
>> 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/[email protected]/
> 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.
[...]
Dietmar Eggemann wrote on 2021/10/25 9:04 下午:
> On 22/10/2021 06:05, Xuewen Yan wrote:
>> Hi Chunguang
>>
>> brookxu <[email protected]> 于2021年10月21日周四 下午4:24写道：
>>>
>>> From: Chunguang Xu <[email protected]>
>>>
>>> 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 <[email protected]>
>>> ---
>>> 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/[email protected]/
>> 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 :)
> [...]
>