Hello,

Antti P Miettinen [off-list ref] writes:

This is a continuation to "RFC: CPU frequency min as PM QoS param"
patchset. This patchset adds CPU frequency maximum as a PM QoS
parameter and modifies CPU frequncy core to enforce the limit. CPU
frequency ceiling can be used to improve the energy efficiency of
workloads that would cause the cpufreq governors to enforce an
unnecessarily high operating point. In other words, CPU frequency
maximum can act as an energy efficiency level request.

Tested on Dell E6420 with the ACPI cpufreq driver against Ubuntu
3.2. Patches are against linux-next, compile tested.

I know there were some earlier discussions about the usefulness of a max
frequency QoS parameter, so I wanted to throw in a reason to include max
as well as min frequency parameters.

IMO, having a max frequency QoS parameter would be very useful from a
thermal perspective.  

There are some ongoing projects in the PM working group at Linaro that
are exploring plugins to the thermal framework that implment a "cooling
device" by capping CPU frequency.  Having a QoS parameter do do this
would be the logical interface.

I also agree with some earlier requests that these should probably be
per-CPU instead of global.  That would make it simple to cap frequency
of one cluster while leaving another alone.

Kevin