Messages in this thread | | | Date | Tue, 18 Oct 2011 10:14:42 +1100 | From | NeilBrown <> | Subject | Re: [RFC][PATCH 2/2] PM / Sleep: Introduce cooperative suspend/hibernate mode |
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On Mon, 17 Oct 2011 14:43:21 -0700 John Stultz <john.stultz@linaro.org> wrote:
> On Tue, 2011-10-18 at 08:19 +1100, NeilBrown wrote: > > On Mon, 17 Oct 2011 12:08:49 -0700 John Stultz <john.stultz@linaro.org> wrote:
> > > Though I also think proposed userland implementations that require > > > communication with all wakeup consumers before suspending (which really, > > > once you get aggressive about suspending when you can, means > > > communicating with all wakeup consumers on every wakeup event) isn't > > > really a good solution either. > > > > I would help me a lot if you could be more specific than "good". Do you mean > > "efficient" or "simple" or "secure" or ... > > Sorry. Efficient is what I mean. Having every task that consumes wakeup > events to have to be scheduled seems like it would unnecessarily slow > the suspend process. > > Although I also don't see how the "its ok to suspend" handshake would > look like from the application's point of view. If the application is > blocking in the kernel on something, I don't think it could respond. So > this would require either signals from the PM demaon or the app to be > sure not to block. It just seems messy. I could just be not getting > something that makes it more elegant, so forgive me if that's the case. > >
Sorry - missed this bit in the previous reply.
Blocking in the kernel would be a problem. But programs that need to respond to events tend to avoid blocking. They usually use an event loop and non-blocking IO, or they use threads so that some part is always ready to respond.
The same requirements would be imposed on a process that responds to wakeup events - it just has to be able to respond to 'about to suspend' events too.
So I don't think it is any more messy then event handling always is (and if you use libevent, most of that is hidden under the carpet anyway).
(and no: not signals. Never signals. Just don't even think about signals. I hate signals. Use poll or equivalents - never signals (unless you cannot avoid them))
NeilBrown
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