Messages in this thread | | | Date | Wed, 10 Apr 2013 11:14:01 +0100 | From | Lorenzo Pieralisi <> | Subject | Re: [RFC PATCH 0/2] cpufreq: Introduce LAB cpufreq governor. |
| |
On Wed, Apr 10, 2013 at 09:44:52AM +0100, Lukasz Majewski wrote:
[...]
> > Have you also looked at the power clamp driver that have similar > > target ? > > I might be wrong here, but in my opinion the power clamp driver is a bit > different: > > 1. It is dedicated to Intel SoCs, which provide special set of > registers (i.e. MSR_PKG_Cx_RESIDENCY [*]), which forces a processor to > enter certain C state for a given duration. Idle duration is calculated > by per CPU set of high priority kthreads (which also program [*] > registers). >
Those registers are used for compensation (ie user asked a given idle ratio but HW stats show a mismatch) and they are not "programmed" they are just read. That code is Intel specific but it can be easily ported to ARM, I did that and most of the code is common with zero dependency on the architecture.
> 2. ARM SoCs don't have such infrastructure, so we depend on SW here.
Well, it is true that most of the SoCs I am working on do not have a programming interface to monitor C-state residency, granted, this is a problem. If those stats can be retrieved somehow (I did that on our TC2 platform) then power clamp can be used on ARM with minor modifications.
Lorenzo
| |