On Mon, Aug 2, 2010 at 5:08 PM, <david@xxxxxxx> wrote: > On Mon, 2 Aug 2010, Paul E. McKenney wrote: > >> On Sun, Aug 01, 2010 at 10:06:34PM -0700, david@xxxxxxx wrote: >>> >>> On Sun, 1 Aug 2010, Arjan van de Ven wrote: >>> >>>> I'm a little worried that this whole "I need to block suspend" is >>>> temporary. Yes today there is silicon from ARM and Intel where suspend >>>> is a heavy operation, yet at the same time it's not all THAT heavy >>>> anymore.... at least on the Intel side it's good enough to use pretty >>>> much all the time (when the screen is off for now, but that's a memory >>>> controller issue more than anything else). I'm pretty sure the ARM guys >>>> will not be far behind. >>> >>> remember that this 'block suspend' is really 'block overriding the >>> fact that there are still runable processes and suspending anyway" >>> >>> having it labeled as 'suspend blocker' or even 'wakelock' makes it >>> sound as if it blocks any attempt to suspend, and I'm not sure >>> that's what's really intended. Itsounds like the normal syspend >>> process would continue to work, just this 'ignore if these other >>> apps are busy' mode of operation would not work. >>> >>> which makes me wonder, would it be possible to tell the normal idle >>> detection mechanism to ignore specific processes when deciding if it >>> should suspend or not? how about only considering processes in one >>> cgroup when deciding to suspend and ignoring all others? >> >> Why not flesh this out and compare it to the draft requirements? >> (I expect to be sending another version by end of day Pacific Time.) >> >> The biggest issue I see right off-hand is that a straightforward >> implementation of your idea would require moving processes from one >> cgroup to another when acquiring or releasing a suspend blocker, which >> from what I understand would be way to heavyweight. On the other hand, >> if acquiring and releasing a suspend blocker does not move the process >> from one cgroup to another, then you need something very like the >> suspend-blocker mechanism to handle those processes that are permitted >> to acquire suspend blockers, and which are thus not a member of the >> cgroup in question. >> >> That said, I did see some hint from the Android guys that it -might- >> be possible to leverage cgroups in the way that you suggest might help >> save power during times when suspend was blocked but (for example) the >> screen was turned off. The idea would be to freeze the cgroup whenever >> the screen blanked, even if suspend was blocked. The biggest issue >> here is that any process that can hold a suspend blocker must never to >> an unconditional wait on any process in this cgroup. Seems to me that >> this should be possible in theory, but the devil would be in the details. >> >> If I am misunderstanding your proposal, please enlighten me! > > you are close, but I think what I'm proposing is actually simpler (assuming > that the scheduler can be configured to generate the appropriate stats) > > my thought was not to move applications between cgroups as they > aquire/release the suspend-block lock, bur rather to say that any > application that you would trust to get the suspend-block lock should be in > cgroup A while all other applications are in cgroup B > > when you are deciding if the system shoudl go to sleep because it is idle, > ignore the activity of all applications in cgroup B > > if cgroup A applications are busy, the system is not idle and should not > suspend. > Triggering suspend from idle has been suggested before. However, idle is not a signal that it is safe to suspend since timers stop in suspend (or the code could temporarily be waiting on a non-wakeup interrupt). If you add suspend blockers or wakelocks to prevent suspend while events you care about are pending, then it does not make a lot of sense to prevent suspend just because the cpu is not idle. > this requires that the applications in cgroup A actually go idle as opposed > to simply releaseing the suspend-block lock, but it would mean that there > are no application changes required for to move a system from the status > "even if it's busy, go ahead ans suspend" to "this application is important, > don't suspend if it's got work to do", it would just be classifying the > application in one cgroup or the other. > > This assumes that an application that you would trust to hold the > suspend-block lock is going to be well behaved (if it isn't, how can you > trust it to not grab the lock inappropriatly?) > > David Lang > -- Arve Hjønnevåg _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
