On Tue, Oct 16, 2012 at 12:33:07AM +0200, Colin Cross wrote: > On Mon, Oct 15, 2012 at 8:59 AM, Stephen Warren <swarren@xxxxxxxxxxxxx> wrote: > > On 10/15/2012 01:56 AM, Joseph Lo wrote: > >> There is still one thing you should know. Because we are planning to > >> upstream "CPUquiet" framework that is a CPU auto hotplug mechanism. It > >> will auto hotplug the CPUs depends on the system is busy or not. So when > >> system is idle, there will be only one CPU online (i.e, CPU0). The > >> secondary CPUs will all be hot plugged (i.e, offline and power gate). We > >> need to think about do we still need coupled cpuidle on Tegra30 if we > >> are going to use "CPUquiet". > > > > CPUquiet isn't relevant at all. First, a user may presumably disable > > CPUquiet's Kconfig option (it had better have one, and the system had > > better work with it disabled). Second, even if CPUquiet is enabled, I > > don't imagine there is a 100% guarantee that hot(un)plug will happen > > before cpuidle kicks in, is there? Finally, is there any guarantee that > > CPUquiet will actually be accepted upstream? > > CPUquiet is a glorified hotplug governor, and hotplug governors have > been widely rejected upstream, so I wouldn't plan on seeing it > accepted. Note that nothing in CPUquiet enforces the use of hotplug. It assumes there is a way to put a CPU in a quiet state which means it doesn't get interrupted, doesn't do any work and doesn't respond to IPIs. Currently only hotplug provides this state, but it's possible to provide a driver which uses a different mechanism to provide the same state. We need this state to be able to switch to the low power cluster which has only 1 CPU. IPIs to non-existing cores would hang the system. Cheers, Peter. -- To unsubscribe from this list: send the line "unsubscribe linux-tegra" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
