[PATCH v1 0/4] cpufreq: Allow drivers to receive more information from the governor

Rafael J. Wysocki
2020-12-07T16:41:13Z

Hi,

This is based on the RFC posted a few days ago:

https://lore.kernel.org/linux-pm/1817571.2o5Kk4Ohv2@kreacher/

The majority of the original cover letter still applies, so let me quote it
here:

Using intel_pstate in the passive mode with HWP enabled, in particular under
the schedutil governor, is still kind of problematic, because it has to assume
that it should not allow the frequency to fall below the one requested by the
governor. For this reason, it translates the target frequency into HWP.REQ.MIN
which generally causes the processor to run a bit too fast.

Moreover, this allows the HWP algorithm to use any frequency between the target
one and HWP.REQ.MAX that corresponds to the policy max limit and some workloads
cause it to go for the max turbo frequency prematurely which hurts energy-
efficiency without improving performance, even though the schedutil governor
itself would not allow the frequency to ramp up so fast.

This patch series attempts to improve the situation by introducing a new driver
callback allowing the driver to receive more information from the governor. In
particular, this allows the min (required) and target (desired) performance
levels to be passed to it and those can be used to give better hints to the
hardware.

There are two additional schedutil patches this time (IMO they kind of make
sense without the other two, even though the first one increases the amount of
memory used by schedutil) and patches [2-3/4] correspond to the two patches
in the RFC, respectively.

Please refer to the patch changelogs for details.

Thanks!