On Mon, Mar 24, 2014 at 05:46:47PM +0000, Rob Herring wrote: > On Thu, Mar 20, 2014 at 1:19 PM, Sebastian Capella > <sebastian.capella@xxxxxxxxxx> wrote: > > On 19 March 2014 10:23, Lorenzo Pieralisi <lorenzo.pieralisi@xxxxxxx> wrote: > >> Rob is asking a property describing hw, and honestly unless we define > >> a power consumption property value (defining what it means will be rather > >> complicated though) I'd rather remove index altogether and use min_residency > >> as a comparison value instead. > > > > I like having a separate ranking for power to sort the states. To me > > it seems that min residency could be ambiguous for this. We could > > have states with inverted min_residencies: where a lower consumption > > state has a lower target residency because the cost is recovered more > > quickly. Such a state might have higher latency for exit, so even > > though the lower min_residency/lower power state is clearly > > preferable, selection of the lower power state may be prevented by > > kernel latency constraints. > > Perhaps you can add the min residency and exit latency times. I do not think we should mix exit latency with power consumption ranking, they are used and define different things. The problem is that min_residency is extremely hard to define (see discussion below). http://www.spinics.net/lists/arm-kernel/msg316147.html What should min_residency represent ? As Anti correctly pointed out, it should be compared to a shallower idle state, but to define "shallower" we need a ranking, do not we ? If we say "min_residency is the time required for the processor to stay in the idle state in order to maximize power savings" (and I tried to do that), that's wrong by definition, because there might be a deeper idle state saving more power when entered for a time within the next event. state 1 - min residency 10 us state 2 - min residency 20 us If we sleep for 1 second, state 2 must be entered, not 1 and the problem is always the same, state 1 10us compares to state 0 (break even time against state 0). So, we are back to square one. How should min_residency be defined ? If it is the break even time against a shallower idle state, we have to know what's the shallower idle state, so we need a power ranking for idle states. > Another piece to consider is the affinity level of the state should > probably be the basis for 1st order sorting. I would like to see the idle states as a flat list, when you say affinity you mean a cpumask ? Affinity level in the PSCI power state parameter ? In the MPIDR ? Thanks, Lorenzo -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
