Messages in this thread | | | Date | Mon, 11 Apr 2022 16:07:14 +0200 | Subject | Re: [PATCH] sched: Take thermal pressure into account when determine rt fits capacity | From | Dietmar Eggemann <> |
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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.
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