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SubjectRe: [PATCH V7 5/7] cpufreq: Register notifiers with the PM QoS framework
On 15-10-19, 23:50, Rafael J. Wysocki wrote:
> On Tue, Oct 15, 2019 at 5:53 PM Rafael J. Wysocki <rafael@kernel.org> wrote:

> > > - Update QoS framework with the knowledge of related CPUs, this has been pending
> > > until now from my side. And this is the thing we really need to do. Eventually
> > > we shall have only a single notifier list for all CPUs of a policy, at least
> > > for MIN/MAX frequencies.
> >
> > - Move the PM QoS requests and notifiers to the new policy CPU on all
> > changes of that. That is, when cpufreq_offline() nominates the new
> > "leader", all of the QoS stuff for the policy needs to go to this one.
>
> Alas, that still will not work, because things like
> acpi_processor_ppc_init() only work accidentally for one-CPU policies.

I am not sure what problem you see here ? Can you please explain a bit more.

> Generally, adding such a PM QoS request to a non-policy CPU simply has
> no effect until it becomes a policy CPU which may be never.

I was thinking maybe we can read the constraints for all CPUs in the
policy->cpus mask in cpufreq_set_policy() and so this part of the problem will
just go away. The only part that would be left is to remove the QoS constraints
properly.

> It looks like using device PM QoS for cpufreq is a mistake in general
> and what is needed is a struct pm_qos_constraints member in struct
> cpufreq_policy and something like
>
> struct freq_pm_qos_request {
> enum freq_pm_qos_req_type type; /* min or max */
> struct plist_node pnode;
> struct cpufreq_policy *policy;
> };
>
> Then, pm_qos_update_target() can be used for adding, updating and
> removing requests.

--
viresh

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