From: Ionela Voinescu <ionela.voinescu@arm.com>
To: Viresh Kumar <viresh.kumar@linaro.org>
Cc: rjw@rjwysocki.net, sudeep.holla@arm.com,
linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] cpufreq,cppc: fix issue when hotplugging out policy->cpu
Date: Fri, 4 Sep 2020 10:43:03 +0100 [thread overview]
Message-ID: <20200904094303.GA10031@arm.com> (raw)
In-Reply-To: <20200904050604.yoar2c6fofcikipp@vireshk-i7>
Hi Viresh,
On Friday 04 Sep 2020 at 10:36:04 (+0530), Viresh Kumar wrote:
[..]
> > /* Per CPU container for runtime CPPC management. */
> > struct cppc_cpudata {
> > - int cpu;
> > struct cppc_perf_caps perf_caps;
> > struct cppc_perf_ctrls perf_ctrls;
> > struct cppc_perf_fb_ctrs perf_fb_ctrs;
>
> With the way things are designed, I believe this is one of the bugs
> out of many.
>
> The structure cppc_cpudata must be shared across all CPUs of the same
> policy, so they all end up using the same set of values for different
> variables. i.e. it shouldn't be a per-cpu thing at all. Just allocate
> it from cpufreq_driver->init and store in policy->driver_data for use
> elsewhere.
>
> That would be a proper fix IMO, we just avoided one of the bugs here
> otherwise.
>
Do you know why it was designed this way in the first place?
I assumed it was designed like this (per-cpu cppc_cpudata structures) to
allow for the future addition of support for the HW_ALL CPPC coordination
type. In that case you can still have PSD (dependency) domains but the
desired performance controls would be per-cpu, with the coordination
done in hardware/firmware. So, in the HW_ALL case you'd end up having
different performance controls even for CPUs in the same policy.
Currently the CPPC driver only supports SW_ANY which is the traditional
cpufreq approach.
Thanks,
Ionela.
> --
> viresh
next prev parent reply other threads:[~2020-09-04 9:43 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-03 11:19 [PATCH] cpufreq,cppc: fix issue when hotplugging out policy->cpu Ionela Voinescu
2020-09-04 5:06 ` Viresh Kumar
2020-09-04 9:43 ` Ionela Voinescu [this message]
2020-09-07 6:11 ` Viresh Kumar
2020-09-22 16:25 ` Ionela Voinescu
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