On Tue, 1 Jun 2010, Arve Hjønnevåg wrote: > 2010/6/1 Thomas Gleixner <tglx@xxxxxxxxxxxxx>: > > > > On Mon, 31 May 2010, Arve Hjønnevåg wrote: > > > >> On Mon, May 31, 2010 at 2:46 PM, Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote: > >> > On Mon, 31 May 2010, James Bottomley wrote: > >> >> > >> >> For MSM hardware, it looks possible to unify the S and C states by doing > >> >> suspend to ram from idle but I'm not sure how much work that is. > >> > > >> > On ARM, it's not rocket science and we have in tree support for this > >> > already (OMAP). I have done the same thing on a Samsung part as a > >> > prove of concept two years ago and it's really easy as the hardware is > >> > sane. Hint: It's designed for mobile devices :) > >> > > >> > >> We already enter the same power state from idle and suspend on msm. In > >> the absence of misbehaving apps, the difference in power consumption > >> is entirely caused by periodic timers in the user-space framework > >> _and_ kernel. It only takes a few timers triggering per second (I > >> think 3 if they do no work) to double the average power consumption on > >> the G1 if the radio is off. We originally added wakelocks because the > >> hardware we had at the time had much lower power consumption in > >> suspend then idle, but we still use suspend because it saves power. > > > > So how do you differentiate between timers which _should_ fire and > > those you do not care about ? > > > > Only alarms are allowed to fire while suspended. > > > We have mechanisms in place to defer timers so the wakeups are > > minimized. If that's not enough we need to revisit. > > > > Deferring the the timers forever without stopping the clock can cause > problems. Our user space code has a lot of timeouts that will trigger > an error if an app does not respond in time. Freezing everything and > stopping the clock while suspended is a lot simpler than trying to > stop individual timers and processes from running. And resume updates timekeeping to account for the slept time. So the only way to get away with that is to sleep under a second or just ignoring the update by avoiding the access to rtc. So how do you keep timekeeping happy ? Thanks, tglx
