[PATCH v2 1/5] arch_topology: Introduce thermal pressure update function

[Bjorn Andersson]

On Thu 28 Oct 00:16 PDT 2021, Lukasz Luba wrote:

> 
> 
> On 10/27/21 7:43 PM, Bjorn Andersson wrote:
> > On Fri 15 Oct 07:45 PDT 2021, Lukasz Luba wrote:
> > > diff --git a/arch/arm64/include/asm/topology.h b/arch/arm64/include/asm/topology.h
> > [..]
> > > +/**
> > > + * topology_thermal_pressure_update() - Update thermal pressure for CPUs
> > > + * @cpus	: The related CPUs for which capacity has been reduced
> > > + * @capped_freq	: The maximum allowed frequency that CPUs can run at
> > 
> > I know this matches what I see in e.g. the Qualcomm cpufreq hw driver,
> > but in what cases will @capped_freq differ from
> > cpufreq_get_hw_max_freq(cpumask_first(cpus))?
> 
> The @capped_freq is the maximum allowed frequency value due to
> thermal reasons, which will always be lower or equal to the value
> returned by cpufreq_get_hw_max_freq()
> (effectively: 'policy->cpuinfo.max_freq').
> 

Read patch 3 and 4 again and now this makes sense to me.

Thanks,
Bjorn

> We limit the frequency (and voltage) of CPU to reduce power (and heat)
> in the passive cooling system. That information is important to us,
> because scheduler needs to know how fast the CPU can go. It cannot
> assume that the speed is always 'policy->cpuinfo.max_freq'. Often
> it's less then that at heavy load or GPU heavy load (the same SoC).
> 
> Regards,
> Lukasz