On 07-10-20, 13:58, Nicola Mazzucato wrote: > Hi Viresh, > > performance controls is what is exposed by the firmware through a protocol that > is not capable of describing hardware (say SCMI). For example, the firmware can > tell that the platform has N controls, but it can't say to which hardware they > are "wired" to. This is done in dt, where, for example, we map these controls > to cpus, gpus, etc. > > Let's focus on cpus. > > Normally we would have N of performance controls (what comes from f/w) > that that correspond to hardware clock/dvfs domains. > > However, some firmware implementations might benefit from having finer > grained information about the performance requirements (e.g. > per-CPU) and therefore choose to present M performance controls to the > OS. DT would be adjusted accordingly to "wire" these controls to cpus > or set of cpus. > In this scenario, the f/w will make aggregation decisions based on the > requests it receives on these M controls. > > Here we would have M cpufreq policies which do not necessarily reflect the > underlying clock domains, thus some s/w components will underperform > (EAS and thermal, for example). > > A real example would be a platform in which the firmware describes the system > having M per-cpu control, and the cpufreq subsystem will have M policies while > in fact these cpus are "performance-dependent" each other (e.g. are in the same > clock domain). If the CPUs are in the same clock domain, they must be part of the same cpufreq policy. > This performance dependency information is essential for some > components that take information from the cpufreq policy. > > To restore functionality we can use the optional node > 'cpu-performance-dependencies' in dt which will provide such dependency > information and we can add a new cpumask 'dependency_cpus' in policy. > > Hope it gives some clarity. Some, but I am still confused :( Can you give a real example, with exact number of CPUs, how they share clocks/voltage domains and what else the firmware needs in terms of performance-domains ? That may make it easier for me to understand it. -- viresh
