Re: Towards eliminating the freezer

Rafael J. Wysocki
2007-07-25T12:15:24Z

On Wednesday, 25 July 2007 00:14, Alan Stern wrote:
> On Tue, 24 Jul 2007, Rafael J. Wysocki wrote:
>
> > > Then device_suspend() can be simplified:
> > >
> > > int device_suspend(pm_message_t state)
> > > {
> > > int error = 0;
> > >
> > > might_sleep();
> > > list_for_each_entry_reverse(dev, &dpm_locked, power.entry) {
> > > error = suspend_device(dev, state);
> > >
> > > if (error) {
> > > printk(KERN_ERR "Could not suspend device %s: "
> > > "error %d%s\n",
> > > kobject_name(&dev->kobj), error,
> > > error == -EAGAIN ? " (please convert to suspend_late)" : "");
> > > break;
> > > }
> > > list_move(&dev->power.entry, &dpm_off);
> >
> > Is that safe with list_for_each_entry_reverse?
>
> No. I guess it'll have to resemble the other code.
>
> > Yes, that looks fine.
> >
> > So, who's writing the patch? ;-)
>
> I can do it. You haven't made any changes to this part of the code,
> have you?

Yes, I have, quite recently. :-)

> My work tends to be based on Linus's tree, not -mm.

At the moment they are pretty much in line, at least as far as this code is
concerned. Anyway, I'm trying to keep track of PM-related patches,
at http://www.sisk.pl/kernel/hibernation_and_suspend/2.6.23-rc1/

> Something to watch out for: With all the extra locking, we run the risk
> of blocking the keventd workqueue. This may or may not matter, but to
> be safe perhaps there should be a new general-purpose workqueue which
> _expects_ to block (or freeze) during suspends. Any work routine that
> involves adding or removing a device should go on the new workqueue.

Yes, this sounds like a good idea. Still, I think we can check if there are
problems with the keventd workqueue alone, first.

> > > Incidentally, what is dpm_mtx for? It doesn't seem to do anything
> > > useful. Is it a relic of the former runtime PM support?
> >
> > I think so. IMO it can be removed.
> >
> > I also think it would be nicer to have all of the functions in
> > drivers/base/power/{main|suspend|resume}.c moved to one file.
>
> Yes, they are all similar enough that there isn't much point keeping
> them separate.

Plus some variables might be made static, like dpm_off or even dpm_list_mtx.

Greetings,
Rafael

--
"Premature optimization is the root of all evil." - Donald Knuth