On Friday 14 August 2009, Zhang Rui wrote:> On Fri, 2009-08-14 at 02:08 +0800, Rafael J. Wysocki wrote:> > On Thursday 13 August 2009, Zhang Rui wrote:> > > On Thu, 2009-08-13 at 05:43 +0800, Rafael J. Wysocki wrote:> > > > On Wednesday 12 August 2009, Alan Stern wrote:> > > > > On Wed, 12 Aug 2009, Rafael J. Wysocki wrote:> > > > > > > > > > > Hi,> > > > > > > > > > > > The following patches introduce a mechanism allowing us to execute device> > > > > > drivers' suspend and resume callbacks asynchronously during system sleep> > > > > > transitions, such as suspend to RAM. The idea is explained in the [1/1] patch> > > > > > message.> > > > > > > > > > > > Comments welcome.> > > > > > > > > > I get the idea. Not bad.> > > > > > > > Thanks!> > > > > > > > > Have you tried it in a serious way? For example, turning on the> > > > > async_suspend flag for every device?> > > > > > > > No, I've only tested it with a few selected drivers. I'm going to try the> > > > "async everyone" scenario, though.> > > > > > > > > In one way it isn't as efficient as it could be. You fire off a bunch> > > > > of async threads and then make many of them wait for parent or child> > > > > devices. They could be doing useful work instead.> > > > > > > are you talking about this scenario, or I find another problem of this> > > approach:> > > there is a part of dpm_list, dev1->dev_aaa->...->dev_bbb->dev2> > > > > > dev2 is dev1's first child.> > > dev1 resume takes 1s> > > dev_aaa~dev_bbb resume takes 0.1s.> > > > > > if we call device_enable_async_suspend(dev1, true) in order to resume> > > device1 asynchronously, the real asynchronous resume only happens> > > between dev1 and dev_aaa to dev_bbb because dev2 needs to wait until> > > dev1 resume finished.> > > > Yes, that's how it works, but I would call it a limitation rather than a> > problem. It partially stems from the fact that __async_schedule() executes> > ptr() synchronously in some circumstances (e.g. async_enabled unset), so the> > suspend and resume callbacks have to be scheduled in the same order, in which> > they would have been called synchronously.> > > > > so kernel schedules dev1 resume in an async thread first, and then takes> > > 0.1s to finish the dev_aaa to dev_bbb resume, and then sleep 0.9s> > > > > > > I kind of agree, but then the patches would be more complicated.> > > > > > > The problem is that we need to invoke device_resume for every device> > > synchronously.> > > > Yes, we do.> > > > > I wonder if we can make the child devices inherit the> > > parent's dev->power.async_suspend flag, so that devices that need to> > > wait are resumed asynchronously, i.e. we never wait/sleep when parsing> > > the dpm_list.> > > > > > this doesn't bring too much benefit in suspend case but it can speed up> > > the resume process a lot.> > > > We can do that at the core level,> > I think you mean we can't do that at the core level. That's correct, sorry for the mistake. > > because there may be dependencies between> > the children the core doesn't know about. Subsystems are free to set> > async_suspend for the entire branches of device hierarchy if they are known> > not to contain any off-tree dependencies, but the core has no information> > about that.> > > hmm, but the current patch doesn't handle the off-tree dependencies> neither.> e.g.> dev1, dev2, dev3> dev2 depends on dev1, dev3 is dev1's first child,> we only promise that dev1 has been resumed before resuming dev3 in the> current proposal. Sure, and that's why I said "if they are known not to contain any off-treedependencies". IOW, if a subsystem (e.g. platform) knows that none of itsdevices have any off-tree dependencies, it can safely set async_suspend forall of them. > anyway, this is not a problem after the pm_connection stuff is> implemented. :) Well, that's going to take some time I guess. Thanks,Rafael_______________________________________________linux-pm mailing listlinux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx://lists.linux-foundation.org/mailman/listinfo/linux-pm
