On Sun, May 22, 2016 at 01:42:52PM -0700, Steve Muckle wrote: > On Sun, May 22, 2016 at 12:39:12PM +0200, Peter Zijlstra wrote: > > On Fri, May 20, 2016 at 05:53:41PM +0530, Shilpasri G Bhat wrote: > > > > > > Below are the comparisons by disabling watchdog. > > > Both schedutil and ondemand have a similar ramp-down trend. And in both > > > the > > > cases I can see that frequency of the cpu is not reduced in deterministic > > > fashion. In a observation window of 30 seconds after running a workload I > > > can > > > see that the frequency is not ramped down on some cpus in the system and > > > are > > > idling at max frequency. > > > > So does it actually matter what the frequency is when you idle? Isn't > > the whole thing clock gated anyway? > > > > Because this seems to generate contradictory requirements, on the one > > hand we want to stay idle as long as possible while on the other hand > > you seem to want to clock down while idle, which requires not being > > idle. > > > > If it matters; should not your idle state muck explicitly set/restore > > frequency? > > AFAIK this is very platform dependent. Some will waste more power than > others when a CPU idles above fmin due to things like resource (bus > bandwidth, shared cache freq etc) voting.
It is also related to static leakage power that depends on the operating voltage (ie higher operating frequencies require higher voltage) so in a way scaling frequency before going idle may not be effective if voltage does not scale too in turn. Lorenzo
