Re: [PATCH 0/6] PM: Asynchronous suspend and resume of devices

From: Rafael J. Wysocki
Date: Thu Aug 27 2009 - 17:17:40 EST

On Thursday 27 August 2009, Alan Stern wrote:
> On Wed, 26 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 changelogs of the first two patches.
> >
> > Comments welcome.
> I've been terribly busy and haven't had a chance to look at this. The
> earlier version seemed to have a bunch of mutual-exclusion issues; are
> they resolved now?

Please be more specific.

> There were also some problems involving unsafe iteration over the dpm_list
> -- remember that devices can be unregistered at any time, not just while
> they are suspending or resuming.

Not at the time we're holding dpm_list_mtx, though.

I don't think there are any unsafe iterations over dpm_list in the patches.

> When a device finishes, instead of having the async thread look for
> another device to work on, I think it would be better to have the
> thread check the dependents of the current device. Those which are
> now ready can be added to a "device-ready" list, which is used to
> direct the actions of new async threads.

Actually, I wanted to avoid adding such a list, because that would be
duplicating of the async framework's actions, to some extent. Yes, we can
duplicate the async framework just for the suspend/resume needs. No, I don't
think it's worth it.

BTW, the patches have been tested on a dual-core box and I haven't seen any
problems with them so far. Also, the testing shows that the waiting for
devices with unsatisfied dependencies is almost eliminated (on my test box
it happens 4-8 times during the entire suspend-resume cycle).

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