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 thisapproach:there is a part of dpm_list, dev1->dev_aaa->...->dev_bbb->dev2
dev2 is dev1's first child.dev1 resume takes 1sdev_aaa~dev_bbb resume takes 0.1s.
if we call device_enable_async_suspend(dev1, true) in order to resumedevice1 asynchronously, the real asynchronous resume only happensbetween dev1 and dev_aaa to dev_bbb because dev2 needs to wait untildev1 resume finished.
so kernel schedules dev1 resume in an async thread first, and then takes0.1s 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 devicesynchronously.I wonder if we can make the child devices inherit theparent's dev->power.async_suspend flag, so that devices that need towait are resumed asynchronously, i.e. we never wait/sleep when parsingthe dpm_list.
this doesn't bring too much benefit in suspend case but it can speed upthe resume process a lot.
Of cause, this is not a problem if we turn on the async_suspend flag forevery device.
> > It would be interesting to invent a way of representing explicitly the > > non-tree dependencies -- assuming there aren't too many of them! (I > > can just hear the TI guys hollering about power and timer domains...)> > I have an idea.> > Every such dependency involves two devices, one of which is a "master"> and the second of which is a "slave", meaning that the "slave" have to be> suspended before the "master" and cannot be resumed before it. In principle> we could give each device two lists of "dependency objects", one containing> "dependency objects" where the device is the "master" and the other containing> "dependency objects" where the device is the "slave". Then, each "dependency> object" could be represented as> > struct pm_connection {> struct device *master;> struct list_head master_hook;> struct device *slave;> struct list_head slave_hook;> };> > Add some locking, helpers for adding / removing "dependency objects" etc.> and it should work. Instead of checking the parent, walk the list of> "masters", instead of walking the list of children, walk the list of "slaves".> > The core could create those objects for parent-child relationships> automatically, the other ones would have to be added by platforms / bus types /> drivers etc.> this sounds great. :)
thanks,rui
> This approach has a problem that it's prone to adding circular dependencies by> mistake, but then I think it would apply to any other approach just as well.> > Best,> Rafael
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