linux-kernel - Re: [PATCH] ACPI: processor: Add QoS requests for all CPUs

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Message-ID: <20191025025343.tyihliza45os3e4r@vireshk-i7>
Date:   Fri, 25 Oct 2019 08:23:43 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:     Linux ACPI <linux-acpi@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ACPI: processor: Add QoS requests for all CPUs

On 25-10-19, 02:41, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 
> The _PPC change notifications from the platform firmware are per-CPU,
> so acpi_processor_ppc_init() needs to add a frequency QoS request
> for each CPU covered by a cpufreq policy to take all of them into
> account.
> 
> Even though ACPI thermal control of CPUs sets frequency limits
> per processor package, it also needs a frequency QoS request for each
> CPU in a cpufreq policy in case some of them are taken offline and
> the frequency limit needs to be set through the remaining online
> ones (this is slightly excessive, because all CPUs covered by one
> cpufreq policy will set the same frequency limit through their QoS
> requests, but it is not incorrect).
> 
> Modify the code in accordance with the above observations.

I am not sure if I understood everything you just said, but I don't
see how things can break with the current code we have.

Both acpi_thermal_cpufreq_init() and acpi_processor_ppc_init() are
called from acpi_processor_notifier() which is registered as a policy
notifier and is called when a policy is created or removed. Even if
some CPUs of a policy go offline, it won't matter as the request for
the policy stays and it will be dropped only when all the CPUs of a
policy go offline.

What am I missing ?

-- 
viresh