Messages in this thread | | | Date | Fri, 4 Sep 2020 10:43:03 +0100 | From | Ionela Voinescu <> | Subject | Re: [PATCH] cpufreq,cppc: fix issue when hotplugging out policy->cpu |
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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
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