From: Dietmar Eggemann <dietmar.eggemann@arm.com>
To: Xuewen Yan <xuewen.yan94@gmail.com>
Cc: Xuewen Yan <xuewen.yan@unisoc.com>,
Lukasz.Luba@arm.com, rafael@kernel.org, viresh.kumar@linaro.org,
mingo@redhat.com, peterz@infradead.org,
vincent.guittot@linaro.org, rostedt@goodmis.org,
linux-kernel@vger.kernel.org, di.shen@unisoc.com
Subject: Re: [PATCH] sched: Take thermal pressure into account when determine rt fits capacity
Date: Mon, 11 Apr 2022 16:07:14 +0200 [thread overview]
Message-ID: <9bb00bcb-f984-1cf6-39aa-c11dcf7f07cb@arm.com> (raw)
In-Reply-To: <CAB8ipk-KenZaVWQwWqVMksQXLP5r19BQ1OGAdmwHRbjwv3qFHg@mail.gmail.com>
On 11/04/2022 10:52, Xuewen Yan wrote:
> HI Dietmar
>
> On Mon, Apr 11, 2022 at 4:21 PM Dietmar Eggemann
> <dietmar.eggemann@arm.com> wrote:
>>
>> On 07/04/2022 07:19, Xuewen Yan wrote:
>>> There are cases when the cpu max capacity might be reduced due to thermal.
>>> Take into the thermal pressure into account when judge whether the rt task
>>> fits the cpu. And when schedutil govnor get cpu util, the thermal pressure
>>> also should be considered.
>>>
>>> Signed-off-by: Xuewen Yan <xuewen.yan@unisoc.com>
>>> ---
>>> kernel/sched/cpufreq_schedutil.c | 1 +
>>> kernel/sched/rt.c | 1 +
>>> 2 files changed, 2 insertions(+)
>>>
>>> diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
>>> index 3dbf351d12d5..285ad51caf0f 100644
>>> --- a/kernel/sched/cpufreq_schedutil.c
>>> +++ b/kernel/sched/cpufreq_schedutil.c
>>> @@ -159,6 +159,7 @@ static void sugov_get_util(struct sugov_cpu *sg_cpu)
>>> struct rq *rq = cpu_rq(sg_cpu->cpu);
>>> unsigned long max = arch_scale_cpu_capacity(sg_cpu->cpu);
>>>
>>> + max -= arch_scale_thermal_pressure(sg_cpu->cpu);
>>
>> max' = arch_scale_cpu_capacity() - arch_scale_thermal_pressure()
>>
>> For the energy part (A) we use max' in compute_energy() to cap sum_util
>> and max_util at max' and to call em_cpu_energy(..., max_util, sum_util,
>> max'). This was done to match (B)'s `policy->max` capping.
>>
>> For the frequency part (B) we have freq_qos_update_request() in:
>>
>> power_actor_set_power()
>> ...
>> cdev->ops->set_cur_state()
>>
>> cpufreq_set_cur_state()
>> freq_qos_update_request() <-- !
>> arch_update_thermal_pressure()
>>
>> restricting `policy->max` which then clamps `target_freq` in:
>>
>> cpufreq_update_util()
>> ...
>> get_next_freq()
>> cpufreq_driver_resolve_freq()
>> __resolve_freq()
>>
>
> Do you mean that the "max" here will not affect the frequency
> conversion, so there is no need to change it?
> But is it better to reflect the influence of thermal here?
I guess your point is that even though max' has no effect on frequency
since QOS caps policy->max anyway, it is still easier to understand the
dependency between schedutil and EAS/EM when it comes to the use of
thermal pressure.
I agree. The way how the "hidden" policy->max capping guarantees that
schedutil and EAS/EM are doing the same even when only the latter uses
max' is not obvious.
I just wanted to mention the historical reason why the code looks like
it does today.
>> [...]
>>
>>> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
>>> index a32c46889af8..d9982ebd4821 100644
>>> --- a/kernel/sched/rt.c
>>> +++ b/kernel/sched/rt.c
>>> @@ -466,6 +466,7 @@ static inline bool rt_task_fits_capacity(struct task_struct *p, int cpu)
>>> max_cap = uclamp_eff_value(p, UCLAMP_MAX);
>>>
>>> cpu_cap = capacity_orig_of(cpu);
>>> + cpu_cap -= arch_scale_thermal_pressure(cpu);
>>>
>>> return cpu_cap >= min(min_cap, max_cap);
>>> }
>>
>> IMHO, this should follow what we do with rq->cpu_capacity
>> (capacity_of(), the remaining capacity for CFS). E.g. we use
>> capacity_of() in find_energy_efficient_cpu() and select_idle_capacity()
>> to compare capacities. So we would need a function like
>> scale_rt_capacity() for RT (minus the rq->avg_rt.util_avg) but then also
>> one for DL (minus rq->avg_dl.util_avg and rq->avg_rt.util_avg).
>
> It's a really good idea. And do you already have the corresponding patch?
> If there is, can you tell me the corresponding link?
No, I don't have any code for this. Should be trivial though. But the
issue is that the update would probably have to be decoupled from CFS
load_balance (update_group_capacity()) and the use cases in RT/DL are
only valid for asymmetric CPU capacity systems.
next prev parent reply other threads:[~2022-04-11 14:07 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-07 5:19 [PATCH] sched: Take thermal pressure into account when determine rt fits capacity Xuewen Yan
2022-04-11 8:21 ` Dietmar Eggemann
2022-04-11 8:52 ` Xuewen Yan
2022-04-11 14:07 ` Dietmar Eggemann [this message]
2022-04-13 13:25 ` Lukasz Luba
2022-04-16 2:47 ` Xuewen Yan
2022-04-19 7:14 ` Vincent Guittot
2022-04-19 12:01 ` Lukasz Luba
2022-04-19 12:51 ` Vincent Guittot
2022-04-19 14:13 ` Lukasz Luba
2022-04-21 8:29 ` Vincent Guittot
2022-04-21 10:57 ` Lukasz Luba
2022-04-26 7:39 ` Vincent Guittot
2022-04-29 9:27 ` Lukasz Luba
2022-04-20 13:51 ` Qais Yousef
2022-04-21 8:07 ` Xuewen Yan
2022-04-21 16:15 ` Qais Yousef
2022-04-25 1:31 ` Xuewen Yan
2022-04-25 16:12 ` Qais Yousef
2022-04-26 2:07 ` Xuewen Yan
2022-04-26 8:09 ` Vincent Guittot
2022-04-26 9:30 ` Qais Yousef
2022-04-26 10:06 ` Vincent Guittot
2022-04-26 13:06 ` Qais Yousef
2022-04-26 9:21 ` Qais Yousef
2022-04-27 1:38 ` Xuewen Yan
2022-04-27 10:58 ` Qais Yousef
2022-05-01 3:20 ` Xuewen Yan
2022-05-03 14:43 ` Qais Yousef
2022-05-09 2:29 ` Xuewen Yan
2022-05-10 14:56 ` Qais Yousef
2022-05-10 17:44 ` Lukasz Luba
2022-05-10 18:44 ` Qais Yousef
2022-05-10 22:03 ` Lukasz Luba
2022-05-14 15:01 ` Xuewen Yan
2022-05-14 23:55 ` Qais Yousef
2022-05-15 0:53 ` [PATCH] sched/rt: Support multi-criterion fitness search for kernel test robot
2022-05-15 1:43 ` kernel test robot
2022-05-19 14:16 ` [sched] 0eee64011b: canonical_address#:#[##] kernel test robot
2022-06-15 10:13 ` [PATCH] sched: Take thermal pressure into account when determine rt fits capacity Qais Yousef
2022-06-15 11:17 ` Xuewen Yan
2022-06-15 13:54 ` Qais Yousef
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