Since ring frequency programming needs consideration of both IA and GT
frequency requests I think keeping the logic
to program the ring frequency table in driver that monitors both IA/GT
busyness and power budgets like intel_ips
will be more appropriate. intel_ips is relying on global load derived
from all CPUs.
I understand that power awareness and busyness based policy might be
trickier but having that as tunable will give better flexibility.
On 1/3/2018 11:51 PM, Yaodong Li wrote:
You are thinking of plugging into intel_pstate to make it smarter
for ia freq transitions?
Yep. This seems a correct step to give some automatic support instead
of parameter/hardcoded multiplier.
Does this mean we should use cpufreq/intel_pstate based approach
instead of the current modparam solution for Gen9?
Some concerns and questions about intel_pstate approach:
a) Currently, we cannot get the accurate pstate/target freq value from
cpufreq in intel_pstate active mode since
these values won't be exported to cpufreq layer, so if we won't
change intel_pstate code then we only can get
the max cpu freq of a new policy.
b) intel_pstate policy is attached to each logic cpu, which means we
will receive policy/freq transition notification
for each logic cpu freq change. One question is how we are going
to decide the freq of the ring? just use the max
cpu freq reported?
c) With the intel_pstate approach we may still run into thermal
throttling, in this case, can a certain cooling device
be triggered to lower the cpu freq?
Thanks and Regards,
-Jackie
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