Messages in this thread | | | From | Vincent Guittot <> | Date | Wed, 16 Jun 2021 21:25:45 +0200 | Subject | Re: [PATCH v4 2/3] sched/fair: Take thermal pressure into account while estimating energy |
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On Wed, 16 Jun 2021 at 19:24, Dietmar Eggemann <dietmar.eggemann@arm.com> wrote: > > On 15/06/2021 18:09, Lukasz Luba wrote: > > > > On 6/15/21 4:31 PM, Dietmar Eggemann wrote: > >> On 14/06/2021 21:11, Lukasz Luba wrote: > > [...] > > >> It's important to highlight that this will only fix this issue between > >> schedutil and EAS when it's due to `thermal pressure` (today only via > >> CPU cooling). There are other places which could restrict policy->max > >> via freq_qos_update_request() and EAS will be unaware of it. > > > > True, but for this I have some other plans. > > As long as people are aware of the fact that this was developed to be > beneficial for `EAS - IPA` integration, I'm fine with this.
I don't think it's only for EAS - IPA. Thermal_pressure can be used by HW throttling like here: https://lkml.org/lkml/2021/6/8/1791
EAS is involved but not IPA
> > [...] > > >> IMHO, this means that this is catered for the IPA governor then. I'm not > >> sure if this would be beneficial when another thermal governor is used? > > > > Yes, it will be, the cpufreq_set_cur_state() is called by > > thermal exported function: > > thermal_cdev_update() > > __thermal_cdev_update() > > thermal_cdev_set_cur_state() > > cdev->ops->set_cur_state(cdev, target) > > > > So it can be called not only by IPA. All governors call it, because > > that's the default mechanism. > > True, but I'm still not convinced that it is useful outside `EAS - IPA`. > > >> The mechanical side of the code would allow for such benefits, I just > >> don't know if their CPU cooling device + thermal zone setups would cater > >> for this? > > > > Yes, it's possible. Even for custom vendor governors (modified clones > > of IPA) > > Let's stick to mainline here ;-) It's complicated enough ... > > [...] > > >> Maybe shorter? > >> > >> struct cpumask *pd_mask = perf_domain_span(pd); > >> - unsigned long cpu_cap = > >> arch_scale_cpu_capacity(cpumask_first(pd_mask)); > >> + int cpu = cpumask_first(pd_mask); > >> + unsigned long cpu_cap = arch_scale_cpu_capacity(cpu); > >> + unsigned long _cpu_cap = cpu_cap - > >> arch_scale_thermal_pressure(cpu); > >> unsigned long max_util = 0, sum_util = 0; > >> - unsigned long _cpu_cap = cpu_cap; > >> - int cpu; > >> - > >> - _cpu_cap -= arch_scale_thermal_pressure(cpumask_first(pd_mask)); > > > > Could be, but still, the definitions should be sorted from longest on > > top, to shortest at the bottom. I wanted to avoid modifying too many > > lines with this simple patch. > > Only if there are no dependencies, but here we have already `cpu_cap -> > pd_mask`. OK, not a big deal. > > [...] > > >> There is IPA specific code in cpufreq_set_cur_state() -> > >> get_state_freq() which accesses the EM: > >> > >> ... > >> return cpufreq_cdev->em->table[idx].frequency; > >> ... > >> > >> Has it been discussed that the `per-PD max (allowed) CPU capacity` (1) > >> could be stored in the EM from there so that code like the EAS wakeup > >> code (compute_energy()) could retrieve this information from the EM? > > > > No, we haven't think about this approach in these patch sets. > > The EM structure given to the cpufreq_cooling device and stored in: > > cpufreq_cdev->em should not be modified. There are a few places which > > receive the EM, but they all should not touch it. For those clients > > it's a read-only data structure. > > > >> And there wouldn't be any need to pass (1) into the EM (like now via > >> em_cpu_energy()). > >> This would be signalling within the EM compared to external signalling > >> via `CPU cooling -> thermal pressure <- EAS wakeup -> EM`. > > > > I see what you mean, but this might cause some issues in the design > > (per-cpu scmi cpu perf control). Let's use this EM pointer gently ;) > > OK, with the requirement that clients see the EM as ro: > > Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
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