On Thursday 19 February 2009, Alan Stern wrote: > On Thu, 19 Feb 2009, Rafael J. Wysocki wrote: > > > > > Again, the decision to trigger automatic suspend has to be based on some > > > > well defined criteria and the (in)activity of devices seems to be one of them. > > > > > > I don't know what criteria the system monitor would use. > > > > I don't know either and this is the whole point. They need to be specified > > somehow and I'm not sure if "we suspend if no one is holding a wakelock" is the > > right approach. > > That isn't really a criterion; it's just a mechanism. All it does is > push the problem back one level. Now the question becomes: When is it > appropriate/necessary to hold a wakelock? > > > > It might have to be platform-specific. The Android people seem to have a > > > pretty good idea of what criteria will work for them. > > > > I'd really like to know in what situations Androind is supposed to suspend > > automatically. > > It might be better to ask in what situations Android is _not_ supposed > to sleep automatically. In other words, in what situations is a > wakelock acquired? Since the whole system is only a phone, this > question should have a reasonably well-defined answer. > > > > Inactivity of devices isn't always a good criterion. There might be a > > > background task which wakes up every few seconds to do something as > > > long as the system is awake, thereby keeping some device always active. > > > The activity from this background task shouldn't prevent an auto-sleep. > > > > In fact there are two problems here. First, there may be a task preventing > > some devices from becoming inactive (like syslog). > > Which means that device inactivity isn't always a good indicator for > auto-sleep. (But then there can be different levels of activity: A > disk should always block auto-sleep while it is carrying out I/O, but > it might not block auto-sleep just because it is spinning.) > > > Second, there may be > > a task waiting for something important to happen, such that automatic suspend > > cannot be triggered while it's waiting. In both cases, IMO, the kernel is not > > in a point to decide whether to suspend or not, because the user space knows > > better. > > That's the whole point behind userspace wakelocks! They provide a > mechanism for userspace to tell the kernel when (as far as userspace is > concerned) it is or is not okay to auto-sleep. Still, one can go further and observe that the user space can in fact start automatic suspend by itself whenever it knows it's appropriate ... Thanks, Rafael _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
