Re: [PATCH] PM / devfreq: Generic cpufreq governor

[Rafael J. Wysocki]

On Sat, Jul 28, 2018 at 5:56 AM, Saravana Kannan <skannan@xxxxxxxxxxxxxx> wrote:
> Many CPU architectures have caches that can scale independent of the CPUs.
> Frequency scaling of the caches is necessary to make sure the cache is not
> a performance bottleneck that leads to poor performance and power. The same
> idea applies for RAM/DDR.
>
> To achieve this, this patch adds a generic devfreq governor that can listen
> to the frequency transitions of each CPU frequency domain and then adjusts
> the frequency of the cache (or any devfreq device) based on the frequency
> of the CPUs.
>
> To decide the frequency of the device, the governor does one of the
> following:
>
> * Uses a CPU frequency to device frequency mapping table
>   - Either one mapping table used for all CPU freq policies (typically used
>     for system with homogeneous cores/clusters that have the same OPPs.
>   - One mapping table per CPU freq policy (typically used for ASMP systems
>     with heterogeneous CPUs with different OPPs)
>
> OR
>
> * Scales the device frequency in proportion to the CPU frequency. So, if
>   the CPUs are running at their max frequency, the device runs at its max
>   frequency.  If the CPUs are running at their min frequency, the device
>   runs at its min frequency. And interpolated for frequencies in between.

While not having looked at the details of the patch yet, I would
change the name of the feature to "Generic cpufreq transition
governor" to make it somewhat less ambiguous.