On 20 January 2012 21:40, Colin Cross <ccross@xxxxxxxxxxx> wrote: > On Fri, Jan 20, 2012 at 12:46 AM, Daniel Lezcano > <daniel.lezcano@xxxxxxxxxx> wrote: >> Hi Colin, >> >> this patchset could be interesting to resolve in a generic way the cpu >> dependencies. >> What is the status of this patchset ? > > I can't do much with it right now, because I don't have any devices > that can do SMP idle with a v3.2 kernel. I've started working on an > updated version that avoids the spinlock, but it might be a while > before I can test and post it. I'm mostly looking for feedback on the > approach taken in this patch, and whether it will be useful for other > SoCs besides Tegra and OMAP4. > Hi Colin, In your patch, you put in safe state (WFI for most of platform) the cpus that become idle and these cpus are woken up each time a new cpu of the cluster becomes idle. Then, the cluster state is chosen and the cpus enter the selected C-state. On ux500, we are using another behavior for synchronizing the cpus. The cpus are prepared to enter the c-state that has been chosen by the governor and the last cpu, that enters idle, chooses the final cluster state (according to cpus' C-state). The main advantage of this solution is that you don't need to wake other cpus to enter the C-state of a cluster. This can be quite worth full when tasks mainly run on one cpu. Have you also think about such behavior when developing the coupled cpuidle driver ? It could be interesting to add such behavior. Regards, Vincent >> Did you have the opportunity to measure the power consumption with and >> without this patchset ? > > Power consumption will be very dependent on the specific SoC in > question. The most important factors are the power savings of the > independent cpuidle state (normally WFI) vs. the hotplug state > (normally 1 cpu in OFF), and the workload being tested. > > On a very idle system, these patches result in the same total power as > hotplugging one cpu and letting the other idle normally. On a 25% > busy system, you might see a slight increase in power, as the best > independent cpuidle state might be WFI, vs 1 cpu in OFF mode in > hotplug. On OMAP4, that difference is small, on the order of 10 mW. > Once you hit the threshold where a hotplug governor would have > hotplugged in the second cpu (lets say 40%), the savings from these > patches are enormous, as you can hit the lowest power state up to 60% > of the time, where the hotplug solution would never be going below WFI > on both cpus. On OMAP4, that can be well over 100 mW. > _______________________________________________ > linux-pm mailing list > linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx > https://lists.linuxfoundation.org/mailman/listinfo/linux-pm _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/linux-pm
