Re: [Patch v4 5/6] thermal/cpu-cooling: Update thermal pressure in case of a maximum frequency capping

Ionela Voinescu
2019-11-01T15:47:24Z

Hi guys,

On Thursday 31 Oct 2019 at 17:38:25 (+0100), Vincent Guittot wrote:
> On Thu, 31 Oct 2019 at 17:29, Dietmar Eggemann <dietmar.eggemann@arm.com> wrote:
> >
> > On 22.10.19 22:34, Thara Gopinath wrote:
> > > Thermal governors can request for a cpu's maximum supported frequency
> > > to be capped in case of an overheat event. This in turn means that the
> > > maximum capacity available for tasks to run on the particular cpu is
> > > reduced. Delta between the original maximum capacity and capped
> > > maximum capacity is known as thermal pressure. Enable cpufreq cooling
> > > device to update the thermal pressure in event of a capped
> > > maximum frequency.
> > >
> > > Signed-off-by: Thara Gopinath <thara.gopinath@linaro.org>
> > > ---
> > > drivers/thermal/cpu_cooling.c | 31 +++++++++++++++++++++++++++++--
> > > 1 file changed, 29 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/thermal/cpu_cooling.c b/drivers/thermal/cpu_cooling.c
> > > index 391f397..2e6a979 100644
> > > --- a/drivers/thermal/cpu_cooling.c
> > > +++ b/drivers/thermal/cpu_cooling.c
> > > @@ -218,6 +218,23 @@ static u32 cpu_power_to_freq(struct cpufreq_cooling_device *cpufreq_cdev,
> > > }
> > >
> > > /**
> > > + * update_sched_max_capacity - update scheduler about change in cpu
> > > + * max frequency.
> > > + * @policy - cpufreq policy whose max frequency is capped.
> > > + */
> > > +static void update_sched_max_capacity(struct cpumask *cpus,
> > > + unsigned int cur_max_freq,
> > > + unsigned int max_freq)
> > > +{
> > > + int cpu;
> > > + unsigned long capacity = (cur_max_freq << SCHED_CAPACITY_SHIFT) /
> > > + max_freq;
> > > +
> > > + for_each_cpu(cpu, cpus)
> > > + update_thermal_pressure(cpu, capacity);
> > > +}
> > > +
> > > +/**
> > > * get_load() - get load for a cpu since last updated
> > > * @cpufreq_cdev: &struct cpufreq_cooling_device for this cpu
> > > * @cpu: cpu number
> > > @@ -320,6 +337,7 @@ static int cpufreq_set_cur_state(struct thermal_cooling_device *cdev,
> > > unsigned long state)
> > > {
> > > struct cpufreq_cooling_device *cpufreq_cdev = cdev->devdata;
> > > + int ret;
> > >
> > > /* Request state should be less than max_level */
> > > if (WARN_ON(state > cpufreq_cdev->max_level))
> > > @@ -331,8 +349,17 @@ static int cpufreq_set_cur_state(struct thermal_cooling_device *cdev,
> > >
> > > cpufreq_cdev->cpufreq_state = state;
> > >
> > > - return dev_pm_qos_update_request(&cpufreq_cdev->qos_req,
> > > - cpufreq_cdev->freq_table[state].frequency);
> > > + ret = dev_pm_qos_update_request
> > > + (&cpufreq_cdev->qos_req,
> > > + cpufreq_cdev->freq_table[state].frequency);
> > > +
> > > + if (ret > 0)
> > > + update_sched_max_capacity
> > > + (cpufreq_cdev->policy->cpus,
> > > + cpufreq_cdev->freq_table[state].frequency,
> > > + cpufreq_cdev->policy->cpuinfo.max_freq);
> > > +
> > > + return ret;
> > > }
> > >
> > > /**
> > >
> >
> > Why not getting rid of update_sched_max_capacity() entirely and call
> > update_thermal_pressure() in cpu_cooling.c directly? Saves one level in
> > the call chain and would mean less code for this feature.
>
> But you add complexity in update_thermal_pressure which now has to
> deal with a cpumask and to compute some frequency ratio
> IMHO, it's cleaner to keep update_thermal_pressure simple as it is now
>

How about removing update_thermal_pressure altogether and doing all the
work in update_sched_max_capacity? That is, have
update_sched_max_capacity compute the capped_freq_ratio, do the
normalization, and set it per_cpu for all CPUs in the frequency domain.
You'll save some calculations that you're now doing in
update_thermal_pressure for each cpu and you avoid shifting back and
forth.

If you're doing so it would be worth renaming update_sched_max_capacity
to something like update_sched_thermal_pressure.

Thanks,
Ionela.

> >
> > Just compile tested on arm64:
> >
> > diff --git a/drivers/thermal/cpu_cooling.c b/drivers/thermal/cpu_cooling.c
> > index 3211b4d3a899..bf36995013b0 100644
> > --- a/drivers/thermal/cpu_cooling.c
> > +++ b/drivers/thermal/cpu_cooling.c
> > @@ -217,23 +217,6 @@ static u32 cpu_power_to_freq(struct
> > cpufreq_cooling_device *cpufreq_cdev,
> > return freq_table[i - 1].frequency;
> > }
> >
> > -/**
> > - * update_sched_max_capacity - update scheduler about change in cpu
> > - * max frequency.
> > - * @policy - cpufreq policy whose max frequency is capped.
> > - */
> > -static void update_sched_max_capacity(struct cpumask *cpus,
> > - unsigned int cur_max_freq,
> > - unsigned int max_freq)
> > -{
> > - int cpu;
> > - unsigned long capacity = (cur_max_freq << SCHED_CAPACITY_SHIFT) /
> > - max_freq;
> > -
> > - for_each_cpu(cpu, cpus)
> > - update_thermal_pressure(cpu, capacity);
> > -}
> > -
> > /**
> > * get_load() - get load for a cpu since last updated
> > * @cpufreq_cdev: &struct cpufreq_cooling_device for this cpu
> > @@ -353,7 +336,7 @@ static int cpufreq_set_cur_state(struct
> > thermal_cooling_device *cdev,
> > cpufreq_cdev->freq_table[state].frequency);
> >
> > if (ret > 0)
> > - update_sched_max_capacity
> > + update_thermal_pressure
> > (cpufreq_cdev->policy->cpus,
> > cpufreq_cdev->freq_table[state].frequency,
> > cpufreq_cdev->policy->cpuinfo.max_freq);
> > diff --git a/include/linux/sched.h b/include/linux/sched.h
> > index 55dfe9634f67..5707813c7621 100644
> > --- a/include/linux/sched.h
> > +++ b/include/linux/sched.h
> > @@ -1985,9 +1985,9 @@ static inline void rseq_syscall(struct pt_regs *regs)
> > #endif
> >
> > #ifdef CONFIG_SMP
> > -void update_thermal_pressure(int cpu, u64 capacity);
> > +void update_thermal_pressure(struct cpumask *cpus, unsigned int cur,
> > unsigned int max);
> > #else
> > -static inline void update_thermal_pressure(int cpu, u64 capacity)
> > +static inline void update_thermal_pressure(struct cpumask *cpus,
> > unsigned int cur, unsigned int max);
> > {
> > }
> > #endif
> > diff --git a/kernel/sched/thermal.c b/kernel/sched/thermal.c
> > index 0da31e12a5ff..691bdd79597a 100644
> > --- a/kernel/sched/thermal.c
> > +++ b/kernel/sched/thermal.c
> > @@ -43,17 +43,16 @@ static DEFINE_PER_CPU(unsigned long, delta_capacity);
> > * the arch_scale_cpu_capacity and capped capacity is stored in per cpu
> > * delta_capacity.
> > */
> > -void update_thermal_pressure(int cpu, u64 capped_freq_ratio)
> > +void update_thermal_pressure(struct cpumask *cpus, unsigned int cur,
> > unsigned int max)
> > {
> > - unsigned long __capacity, delta;
> > + int cpu;
> >
> > - /* Normalize the capped freq ratio */
> > - __capacity = (capped_freq_ratio * arch_scale_cpu_capacity(cpu)) >>
> > -
> > SCHED_CAPACITY_SHIFT;
> > - delta = arch_scale_cpu_capacity(cpu) - __capacity;
> > - pr_debug("updating cpu%d thermal pressure to %lu\n", cpu, delta);
> > + for_each_cpu(cpu, cpus) {
> > + unsigned long scale_cap = arch_scale_cpu_capacity(cpu);
> > + unsigned long cur_cap = cur * scale_cap / max;
> >
> > - per_cpu(delta_capacity, cpu) = delta;
> > + per_cpu(delta_capacity, cpu) = scale_cap - cur_cap;
> > + }
> > }