+.. SPDX-License-Identifier: GPL-2.0
+
================
CPU Idle Cooling
================
dynamic leakage for this period (modulo the energy needed to enter
this state). So the sustainable power with idle cycles has a linear
relation with the OPP’s sustainable power and can be computed with a
-coefficient similar to:
+coefficient similar to::
Power(IdleCycle) = Coef x Power(OPP)
--------------------
When we reach the thermal trip point, we have to sustain a specified
-power for a specific temperature but at this time we consume:
+power for a specific temperature but at this time we consume::
Power = Capacitance x Voltage^2 x Frequency x Utilisation
fixed value, ‘Voltage’ and the ‘Frequency’ are fixed artificially
because we don’t want to change the OPP. We can group the
‘Capacitance’ and the ‘Utilisation’ into a single term which is the
-‘Dynamic Power Coefficient (Cdyn)’ Simplifying the above, we have:
+‘Dynamic Power Coefficient (Cdyn)’ Simplifying the above, we have::
Pdyn = Cdyn x Voltage^2 x Frequency
tree. So with the idle injection mechanism, we want an average power
(Ptarget) resulting in an amount of time running at full power on a
specific OPP and idle another amount of time. That could be put in a
-equation:
+equation::
P(opp)target = ((Trunning x (P(opp)running) + (Tidle x P(opp)idle)) /
(Trunning + Tidle)
At this point if we know the running period for the CPU, that gives us
the idle injection we need. Alternatively if we have the idle
-injection duration, we can compute the running duration with:
+injection duration, we can compute the running duration with::
Trunning = Tidle / ((P(opp)running / P(opp)target) - 1)
target residency, otherwise we end up consuming more energy and
potentially invert the mitigation effect
-So the final equation is:
+So the final equation is::
Trunning = (Tidle - Twakeup ) x
(((P(opp)dyn + P(opp)static ) - P(opp)target) / P(opp)target )