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. Alan Stern _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
