Messages in this thread | | | Date | Tue, 26 Feb 2019 10:00:28 +0000 | From | Qais Yousef <> | Subject | Re: [PATCH V2 4/5] cpufreq: Register notifiers with the PM QoS framework |
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On 02/26/19 08:00, Viresh Kumar wrote: > On 25-02-19, 12:14, Qais Yousef wrote: > > On 02/25/19 14:39, Viresh Kumar wrote: > > > On 25-02-19, 08:58, Qais Yousef wrote: > > > > On 02/25/19 10:01, Viresh Kumar wrote: > > > > > > > + min = dev_pm_qos_read_value(cpu_dev, DEV_PM_QOS_MIN_FREQUENCY); > > > > > > > + max = dev_pm_qos_read_value(cpu_dev, DEV_PM_QOS_MAX_FREQUENCY); > > > > > > > + > > > > > > > + if (min > new_policy->min) > > > > > > > + new_policy->min = min; > > > > > > > + if (max < new_policy->max) > > > > > > > + new_policy->max = max; > > > > > > > And this is why we need to check here if the PM QoS value doesn't conflict with > > > > the current min/max, right? Until the current notifier code is removed they > > > > could trip over each others. > > > > > > No. The above if/else block is already removed as part of patch 5/5. It was > > > required because of conflict between userspace specific min/max and qos min/max, > > > which are migrated to use qos by patc 5/5. > > > > > > The cpufreq notifier mechanism already lets users play with min/max and that is > > > already safe from conflicts. > > > > > > > > > > It would be nice to add a comment here about PM QoS managing and remembering > > > > values > > > > > > I am not sure if that would add any value. Some documentation update may be > > > useful for people looking for details though, that I shall do after all the > > > changes get in and things become a bit stable. > > > > > > > Up to you. But not everyone is familiar with the code and a one line comment > > that points to where aggregation is happening would be helpful for someone > > scanning this code IMHO. > > Okay, will add something then. > > > > > and that we need to be careful that both mechanisms don't trip over > > > > each others until this transient period is over. > > > > > > The second mechanism will die very very soon once this is merged, migrating them > > > shouldn't be a big challenge AFAICT. I didn't attempt that because I didn't > > > wanted to waste time updating things in case this version also doesn't make > > > sense to others. > > > > > > > I have a nit too. It would be nice to explicitly state this is > > > > CPU_{MIN,MAX}_FREQUENCY. I can see someone else adding {MIN,MAX}_FREQUENCY for > > > > something elsee (memory maybe?) > > > > > > This is not CPU specific, but any device. The same interface shall be used by > > > devfreq as well, who wanted to use freq-constraints initially. > > > > > > > I don't get that to be honest. I probably have to read more. > > > > Is what you're saying that when applying a MIN_FREQUENCY constraint the same > > value will be applied to both cpufreq and devfreq? Isn't this too coarse? > > Oh no. A constraint with QoS is added like this: > > dev_pm_qos_add_request(dev, req, DEV_PM_QOS_MIN_FREQUENCY, min); > > Now dev here can be any device struct, CPU's or GPU's or anything else. All the > MIN freq requests are stored/processed per device and for a CPU in cpufreq all > we will see is MIN requests for the CPUs. And so the macro is required to be a > bit generic and shouldn't have CPU word within it. > > Hope I was able to clarify your doubt a bit. Thanks.
Ah I see yes it all makes sense now.
Thanks!
-- Qais Yousef
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