On Wed, May 14, 2008 at 11:18:37AM -0400, Len Brown wrote: > On Wednesday 14 May 2008, Matthew Garrett wrote: > > Check processor_thermal.c. It explicitly interfaces with cpufreq in > > order to perform P state management. > > The hook above is so that ACPI thermal throttling > does not invoke T-states until the more efficient > P-states have already been exhausted. > > It doesn't imply the presence of thermal awareness > anywhere in the cpufreq sub-system. The cpufreq sub-system itself isn't aware of thermal issues, but the ACPI system is. I'm not sure that the distinction's especially important. > It also doesn't imply that running cpufreq on top > of T-states is a good idea. Cpufreq as implemented, > say by the ondemand governor, is based > on the assumption that it is running on top of > P-states. Deeper P-states result in > more efficient operation (less energy/instruction) > due to their lower voltage, because energy varies with voltage^2. > T-states violate that assumpion and provide > all the performance cost with none of the efficiency > gains of P-states, because energy varies directly > with frequencey -- but so does performance cost. Right. I'm not implying that this is a desirable situation, but the fact remains that some machines will reach critical shutdown temperature unless something is done to reduce the speed of the processor. If you don't have P states or ACPI-exposed T states, then p4-clockmod is about the best you can manage. > > > There is already a well known thermal throttling interface > > > available via ACPI and it does not need p4_clockmod to run. > > > Passive trip points work automatically even without cpufreq being present. > > > If they do not, then we need to fix them. > > > > You're assuming that the throttling interface is always exposed via > > ACPI. I've seen machines where this isn't the case. > > Please show me those machines. http://www.google.co.uk/search?hl=en&client=firefox-a&rls=org.mozilla%3Aen-US%3Aofficial&hs=R8P&q=acpi+throttling+";<not+supported>"+-C3&btnG=Search&meta= (a lot of false positives, but many of these are genuine) -- Matthew Garrett | mjg59@xxxxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
