Timo, Holger, Andi pointed me to your FOSDEM Linux Power Management presentation: http://en.opensuse.org/FOSDEM2006 http://files.opensuse.org/opensuse/en/b/b5/One_step_opendesign.pdf And I'm glad to see you working on Linux Power Management. But I'm a little concerned that user-space and the kernel are a little out of sync on a few things. I'm happy to see that the userspace p-state governor is no longer enabled by default on SuSE systems. While it was passable on servers with steady-state workloads, it was very bad for laptops where the machine spends a lot of time idle, but has short bursts of processing need which userspace could not detect. These laptops would spend virtually all their time in Pn when using the userspace governor. The next step is to delete the userspace governor as a valid governor selection entirely. If somebody really wants manual control, they can still set the limits within which "ondemand" will stay. I'm happy to see that clock throttling is not enabled by default in recent SuSE release, at least on my laptop which supports P-states. I'd like to see no option to enable clock-throttling on systems that support real p-states. It is useful only for workloads which have an infinite amount of non-idle computing which you don't care how slow it computes. For the vast majority of workloads it just slows down the machine and delays the processor from getting into idle where it can save a non-linear amount of power. Further, there exist today systems which will consume MORE power in deep C-states when throttled vs. when not throttled. The other major topic is the user/kernel interface for power management policy. there needs to be in-kernel state for this, else the device drivers will have no low-latency way to get the answer to the simple policy question of how they should optimize for performance vs power at any given instant when they recognize their device is idle.. this state should be controlled by user space, but I think it is most practical for it to be kernel resident. thanks, -Len - To unsubscribe from this list: send the line "unsubscribe linux-laptop" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
