Arve Hjønnevåg <arve@xxxxxxxxxxx> writes: > 2009/5/6 Kevin Hilman <khilman@xxxxxxxxxxxxxxxxxxx>: >> Arve Hjønnevåg <arve@xxxxxxxxxxx> writes: >> >>> This patch series adds a suspend-block api that provides the same >>> functionality as the android wakelock api. This patch series removes >>> the sysdev that was used to abort suspend and adds a direct check in >>> suspend_enter instead. It also has some other code style changes. >> >> Sorry for joining the wakelock/suspend-block discussion a bit late, >> but I have a very basic, and possibly stupid question on the need for >> such a feature. >> >> My basic question: is why not use idle (dynamic PM) instead of suspend >> (static PM) for this? >> > > We use suspend in addition to idle, not instead of. On some systems > (msm) we can enter the same power state from idle as from suspend. > This reduces the importance of suspend, but entering suspend still has > benefits. The monotonic clock stops and all the periodic timers > (user-space and kernel) that are based on it stop with it. It also > reduces the amount of energy an untrusted application can waste since > it will not be allowed to run when the system is suspended. > >> IOW, why not use CPUidle + PM QoS to achieve the same goal? It seems >> to me that you're trying to add some dynamic PM features onto a static >> PM subsystem. I could see PM QoS possibly needing some extending but >> the basic abilities to constrain the low-power states are there. > > suspend blockers have no impact on this. > >> The one reason I can think of is that you can always have broken >> drivers or apps that prevent you from hitting idle. But with tools >> like powertop, it's pretty easy to find these problems and fix them. >> > Tools allow you to find apps that waste power, but they do not fix them. > >> If that is the primary concern, it seems to me that we're introducing >> a new kernel API to work around broken drivers and apps that should be >> fixed instead. >> >> What am I missing? > > Suspend blockers allow you to use suspend. On platforms that cannot > enter the same power state from idle this is essential. On platforms > can enter the same power state from idle as suspend, suspend reduce > the time spent running which in turn reduces the overall power draw. > It also offers some protection against bad apps which is important on > an open device. Arve, Thanks for the clarifications. Like Mark, I feel like I have a better grip on the motivation behind these changes. Thanks, Kevin _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
