Hi! > --- /dev/null > +++ b/Documentation/thermal/cpu-idle-cooling.txt > @@ -0,0 +1,165 @@ > + > +Situation: > +---------- > + Can we have some real header here? Also if this is .rst, maybe it should be marked so? > +Under certain circumstances, the SoC reaches a temperature exceeding > +the allocated power budget or the maximum temperature limit. The I don't understand. Power budget is in W, temperature is in kelvin. Temperature can't exceed power budget AFAICT. > +former must be mitigated to stabilize the SoC temperature around the > +temperature control using the defined cooling devices, the latter later? > +catastrophic situation where a radical decision must be taken to > +reduce the temperature under the critical threshold, that can impact > +the performances. performance. > +Another situation is when the silicon reaches a certain temperature > +which continues to increase even if the dynamic leakage is reduced to > +its minimum by clock gating the component. The runaway phenomena will > +continue with the static leakage and only powering down the component, > +thus dropping the dynamic and static leakage will allow the component > +to cool down. This situation is critical. Critical here, critical there. I have trouble following it. Theoretically hardware should protect itself, because you don't want kernel bug to damage your CPU? > +Last but not least, the system can ask for a specific power budget but > +because of the OPP density, we can only choose an OPP with a power > +budget lower than the requested one and underuse the CPU, thus losing > +performances. In other words, one OPP under uses the CPU with a performance. > +lesser than the power budget and the next OPP exceed the power budget, > +an intermediate OPP could have been used if it were present. was. > +Solutions: > +---------- > + > +If we can remove the static and the dynamic leakage for a specific > +duration in a controlled period, the SoC temperature will > +decrease. Acting at the idle state duration or the idle cycle "should" decrease? If you are in bad environment.. > +The Operating Performance Point (OPP) density has a great influence on > +the control precision of cpufreq, however different vendors have a > +plethora of OPP density, and some have large power gap between OPPs, > +that will result in loss of performance during thermal control and > +loss of power in other scenes. scene seems to be wrong word here. > +At a specific OPP, we can assume injecting idle cycle on all CPUs, Extra comma? > +Idle Injection: > +--------------- > + > +The base concept of the idle injection is to force the CPU to go to an > +idle state for a specified time each control cycle, it provides > +another way to control CPU power and heat in addition to > +cpufreq. Ideally, if all CPUs of a cluster inject idle synchronously, > +this cluster can get into the deepest idle state and achieve minimum > +power consumption, but that will also increase system response latency > +if we inject less than cpuidle latency. I don't understand last sentence. > +The mitigation begins with a maximum period value which decrease decreases? > +more cooling effect is requested. When the period duration is equal > to > +the idle duration, then we are in a situation the platform can’t > +dissipate the heat enough and the mitigation fails. In this case fast enough? > +situation is considered critical and there is nothing to do. The idle Nothing to do? Maybe power the system down? > +The idle injection duration value must comply with the constraints: > + > +- It is lesser or equal to the latency we tolerate when the mitigation less ... than the latency > +Minimum period > +-------------- > + > +The idle injection duration being fixed, it is obvious the minimum > +period can’t be lesser than that, otherwise we will be scheduling the less. > +Practically, if the running power is lesses than the targeted power, less. > +However, in this demonstration we ignore three aspects: > + > + * The static leakage is not defined here, we can introduce it in the > + equation but assuming it will be zero most of the time as it is , but? Best regards, Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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