Messages in this thread | | | Subject | Re: [PATCH v3 3/3] [RFC] CPUFreq: Add support for cpu-perf-dependencies | From | Lukasz Luba <> | Date | Fri, 6 Nov 2020 10:37:51 +0000 |
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Hi Viresh,
On 11/6/20 9:20 AM, Viresh Kumar wrote: > On 02-11-20, 12:01, Nicola Mazzucato wrote: >> This is a continuation of the previous v2, where we focused mostly on the >> dt binding. >> >> I am seeking some feedback/comments on the following two approaches. >> >> Intro: >> We have seen that in a system where performance control and hardware >> description do not match (i.e. per-cpu), we still need the information of >> how the v/f lines are shared among the cpus. We call this information >> "performance dependencies". >> We got this info through the opp-shared (the previous 2 patches aim for >> that). >> >> Problem: >> How do we share such info (retrieved from a cpufreq driver) to other >> consumers that rely on it? I have two proposals. > > I haven't really stop thinking about what and how we should solve > this, but I have few concerns first. > >> 2) drivers/thermal/cpufreq_cooling: Replace related_cpus with dependent_cpus > > I am not sure if I understand completely on how this is going to be > modified/work. > > The only use of related_cpus in the cooling driver is in the helper > cdev->get_requested_power(), where we need to find the total power > being consumed by devices controlled by the cooling device. Right ? > > Now the cooling devices today are very closely related to the cpufreq > policy, the registration function itself takes a cpufreq policy as an > argument. > > Consider that you have an octa-core platform and all the CPUs are > dependent on each other. With your suggested changes and hw control, > we will have different cpufreq policies for each CPU. And so we will > have a cooling device, cdev, for each CPU as well. When the IPA > governor calls cdev->get_requested_power(), why should we ever bother > to traverse the list of dependent_cpus and not related_cpus only ? > > Otherwise the same CPU will have its load contributed to the power of > 8 cooling devices. >
Good question.
How about a different interface for those cpufreq drivers? That new registration API would allow to specify the cpumask. Or rely on EM cpumask: em_span_cpus(em)
Currently we have two ways to register cooling device: 1. when the cpufreq driver set a flag CPUFREQ_IS_COOLING_DEV, the core will register cooling device 2. cpufreq driver can explicitly call the registration function: cpufreq_cooling_register() with 'policy' as argument
That would need substantial change to the cpufreq cooling code, from policy oriented to custom driver's cpumask (like EM registration).
Regards, Lukasz
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