linux-kernel - Re: [PATCH V7 5/7] cpufreq: Register notifiers with the PM QoS framework

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Message-ID: <20191016082742.nttzuofes6uds4pu@vireshk-i7>
Date:   Wed, 16 Oct 2019 13:57:42 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Dmitry Osipenko <digetx@...il.com>,
        Rafael Wysocki <rjw@...ysocki.net>,
        Linux PM <linux-pm@...r.kernel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Matthias Kaehlcke <mka@...omium.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Pavel Machek <pavel@....cz>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-tegra <linux-tegra@...r.kernel.org>
Subject: Re: [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@...nel.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