On 08/11/2021 09:49, Xuewen Yan wrote:
> Hi Dietmar
>
> On Sat, Nov 6, 2021 at 1:20 AM Dietmar Eggemann
> <dietmar.eggemann@xxxxxxx> wrote:
>>
>> On 05/11/2021 06:58, Zhaoyang Huang wrote:
>>>> I don't understand the EAS (probably asymmetric CPU capacity is meant
>>>> here) angle of the story. Pressure on CPU capacity which is usable for
>>>> CFS happens on SMP as well?
>>> Mentioning EAS here mainly about RT tasks preempting small CFS tasks
>>> (big CFS tasks could be scheduled to big core), which would introduce
>>> more proportion of preempted time within PSI_MEM_STALL than SMP does.
>>
>> What's your CPU layout? Do you have the little before the big CPUs? Like
>> Hikey 960?
[...]
>> And I guess rt class prefers lower CPU numbers hence you see this?
>>
> our CPU layout is:
> xuewen.yan:/ # cat /sys/devices/system/cpu/cpu*/cpu_capacity
> 544
> 544
> 544
> 544
> 544
> 544
> 1024
> 1024
>
> And in our platform, we use the kernel in mobile phones with Android.
> And we prefer power, so we prefer the RT class to run on little cores.
Ah, OK, out-of-tree extensions.
[...]
>>>>>>>> + if (current->in_memstall)
>>>>>>>> + growth_fixed = div64_ul((1024 - rq->avg_rt.util_avg - rq->avg_dl.util_avg
>>>>>>>> + - rq->avg_irq.util_avg + 1) * growth, 1024);
>>>>>>>> +
>>>>
>>>> We do this slightly different in scale_rt_capacity() [fair.c]:
>>>>
>>>> max = arch_scale_cpu_capacity(cpu_of(rq) /* instead of 1024 to support
>>>> asymmetric CPU capacity */
>>> Is it possible that the SUM of rqs' util_avg large than
>>> arch_scale_cpu_capacity because of task migration things?
>>
>> I assume you meant if the rq (cpu_rq(CPUx)) util_avg sum (CFS, RT, DL,
>> IRQ and thermal part) can be larger than arch_scale_cpu_capacity(CPUx)?
>>
>> Yes it can.
>>
>> Have a lock at
>>
>> effective_cpu_util(..., max, ...) {
>>
>> if (foo >= max)
>> return max;
>>
>> }
>>
>> Even the CFS part (cpu_rq(CPUx)->cfs.avg.util_avg) can be larger than
>> the original cpu capacity (rq->cpu_capacity_orig).
>>
>> Have a look at cpu_util(). capacity_orig_of(CPUx) and
>> arch_scale_cpu_capacity(CPUx) both returning rq->cpu_capacity_orig.
>>
>
> Well, your means is we should not use the 1024 and should use the
> original cpu capacity?
> And maybe use the "sched_cpu_util()" is a good choice just like this:
>
> + if (current->in_memstall)
> + growth_fixed = div64_ul(cpu_util_cfs(rq) * growth,
> sched_cpu_util(rq->cpu, capacity_orig_of(rq->cpu)));
Not sure about this. In case util_cfs=0 you would get scale=0.
IMHO, you need
cap = rq->cpu_capacity
cap_orig = rq->cpu_capacity_orig
scale = (cap * X) / cap_orig
or if the update of these rq values happens to infrequently for you then
you have to calc the pressure evey time. Something like:
pressure = cpu_util_rt(rq) + cpu_util_dl(rq)
irq = cpu_util_irq(rq)
if (irq >= cap_orig)
pressure = cap_orig
else
pressure = scale_irq_capacity(pressure, irq, cap_orig)
pressure += irq
scale = ((cap_orig - pressure) * X) / cap_orig
