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.
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.
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.
Of cause, this is not a problem if we turn on the async_suspend flag for
every 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
--
To unsubscribe from this list: send the line "unsubscribe linux-acpi" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
