cpufreq: intel_pstate: EAS support for hybrid platforms

Modify intel_pstate to register EM perf domains for CPUs on hybrid
platforms without SMT which causes EAS to be enabled on them when
schedutil is used as the cpufreq governor (which requires intel_pstate
to operate in the passive mode).

This change is targeting platforms (for example, Lunar Lake) where the
"little" CPUs (E-cores) are always more energy-efficient than the "big"
or "performance" CPUs (P-cores) when run at the same HWP performance
level, so it is sufficient to tell EAS that E-cores are always preferred
(so long as there is enough spare capacity on one of them to run the
given task).  However, migrating tasks between CPUs of the same type
too often is not desirable because it may hurt both performance and
energy efficiency due to leaving warm caches behind.

For this reason, register a separate perf domain for each CPU and choose
the cost values for them so that the cost mostly depends on the CPU type,
but there is also a small component of it depending on the performance
level (utilization) which helps to balance the load between CPUs of the
same type.

The cost component related to the CPU type is computed with the help of
the observation that the IPC metric value for a given CPU is inversely
proportional to its performance-to-frequency scaling factor and the cost
of running code on it can be assumed to be roughly proportional to that
IPC ratio (in principle, the higher the IPC ratio, the more resources
are utilized when running at a given frequency, so the cost should be
higher).

For all CPUs that are online at the system initialization time, EM perf
domains are registered when the driver starts up, after asymmetric
capacity support has been enabled.  For the CPUs that become online
later, EM perf domains are registered after setting the asymmetric
capacity for them.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Tested-by: Christian Loehle <christian.loehle@arm.com>
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Link: https://patch.msgid.link/6057101.MhkbZ0Pkbq@rjwysocki.net

0 files changed, 0 insertions, 0 deletions