On Tue, 2009-05-19 at 15:01 -0400, Len Brown wrote: > > ... the point is, we > > don't need a new interface to force a cpu idle. Hotplug does that. > > > > Furthermore, we should not want anything outside of that, either the cpu > > is there available for work, or its not -- halfway measures don't make > > sense. > > > > Furthermore, we already have power aware scheduling which tries to > > aggregate idle time on cpu/core/packages so as to maximize the idle time > > power savings. Use it there. > > Some context... <snip default story of thermal overcommit> > > > > Besides, a hot removed cpu will do a dead loop halt, which isn't power saving > > > > efficient. To make hot removed cpu enters deep C-state is in whish list for a > > > > long time, but still not available. The acpi_processor_idle is a module, and > > > > cpuidle governor potentially can't handle offline cpu. > > > > > > Then fix that hot-unplug idle loop. I agree that the hlt thing is silly, > > > and I've no idea why its still there, seems like a much better candidate > > > for your efforts than this. > > CONFIG_HOTPLUG_CPU has been problematic in the past. > It does more than what we need here, so we thought > a lighter-weight and lower-latency method that simply > didn't schedule to the idled cpu would suffice. > We are fixing the hotplug-unplug idle loop, but there > turns out to be some issues with it related to idle > processors with interrupts disabled that don't actually > get down into the deep C-states we request:-( > > So this is why you see a patch for a "halfway measure", > it does what is necessary, and does nothing more. Its broken, its ill-defined and its not going to happen. Ripping cpus out of the top cpuset might upset the cpuset configuration and has no regards for any realtime processes. And I must take back my earlier suggestion, hotplug is a bad solution too. There's just too much user policy (cpuset configuration) to upset. The IBM folks are working on a scheduler based solution, please talk to them. -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
