Re: Async suspend-resume patch w/ completions (was: Re: Async suspend-resume patch w/ rwsems)

Rafael J. Wysocki
2009-12-19T23:09:43Z

On Saturday 19 December 2009, Dmitry Torokhov wrote:
> On Dec 19, 2009, at 1:33 PM, "Rafael J. Wysocki" <rjw@sisk.pl> wrote:
>
> > On Saturday 19 December 2009, Dmitry Torokhov wrote:
> >> On Fri, Dec 18, 2009 at 11:43:29PM +0100, Rafael J. Wysocki wrote:
> >>> On Wednesday 16 December 2009, Dmitry Torokhov wrote:
> >>>> On Wed, Dec 16, 2009 at 03:11:05AM +0100, Rafael J. Wysocki wrote:
> >>>>> On Tuesday 15 December 2009, Linus Torvalds wrote:
> >>>>>>
> >>>>>> On Tue, 15 Dec 2009, Rafael J. Wysocki wrote:
> >>>>>>>>
> >>>>>>>> Give a real example that matters.
> >>>>>>>
> >>>>>>> I'll try. Let -> denote child-parent relationships and assume
> >>>>>>> dpm_list looks
> >>>>>>> like this:
> >>>>>>
> >>>>>> No.
> >>>>>>
> >>>>>> I mean something real - something like
> >>>>>>
> >>>>>> - if you run on a non-PC with two USB buses behind non-PCI
> >>>>>> controllers.
> >>>>>>
> >>>>>> - device xyz.
> >>>>>>
> >>>>>>> If this applies to _resume_ only, then I agree, but the
> >>>>>>> Arjan's data clearly
> >>>>>>> show that serio devices take much more time to suspend than USB.
> >>>>>>
> >>>>>> I mean in general - something where you actually have hard data
> >>>>>> that some
> >>>>>> device really needs anythign more than my one-liner, and really
> >>>>>> _needs_
> >>>>>> some complex infrastructure.
> >>>>>>
> >>>>>> Not "let's imagine a case like xyz".
> >>>>>
> >>>>> As I said I would, I made some measurements.
> >>>>>
> >>>>> I measured the total time of suspending and resuming devices as
> >>>>> shown by the
> >>>>> code added by this patch:
> >>>>> http://git.kernel.org/?p=linux/kernel/git/rafael/suspend-2.6.git;a=commitdiff_plain;h=c1b8fc0a8bff7707c10f31f3d26bfa88e18ccd94;hp=087dbf5f079f1b55cbd3964c9ce71268473d5b67
> >>>>> on two boxes, HP nx6325 and MSI Wind U100 (hardware-wise they
> >>>>> are quite
> >>>>> different and the HP was running 64-bit kernel and user space).
> >>>>>
> >>>>> I took four cases into consideration:
> >>>>> (1) synchronous suspend and resume (/sys/power/pm_async = 0)
> >>>>> (2) asynchronous suspend and resume as introduced by the async
> >>>>> branch at:
> >>>>> http://git.kernel.org/?p=linux/kernel/git/rafael/suspend-2.6.git;a=shortlog;h=refs/heads/async
> >>>>> (3) asynchronous suspend and resume like in (2), but with your
> >>>>> one-liner setting
> >>>>> the power.async_suspend flag for PCI bridges on top
> >>>>> (4) asynchronous suspend and resume like in (2), but with an
> >>>>> extra patch that
> >>>>> is appended on top
> >>>>>
> >>>>> For those tests I set power.async_suspend for all USB devices,
> >>>>> all serio input
> >>>>> devices, the ACPI battery and the USB PCI controllers (to see
> >>>>> the impact of the
> >>>>> one-liner, if any).
> >>>>>
> >>>>> I carried out 5 consecutive suspend-resume cycles (started from
> >>>>> under X) on
> >>>>> each box in each case, and the raw data are here (all times in
> >>>>> milliseconds):
> >>>>> http://www.sisk.pl/kernel/data/async-suspend.pdf
> >>>>>
> >>>>> The summarized data are below (the "big" numbers are averages
> >>>>> and the +/-
> >>>>> numbers are standard deviations, all in milliseconds):
> >>>>>
> >>>>> HP nx6325 MSI Wind U100
> >>>>>
> >>>>> sync suspend 1482 (+/- 40) 1180 (+/- 24)
> >>>>> sync resume 2955 (+/- 2) 3597 (+/- 25)
> >>>>>
> >>>>> async suspend 1553 (+/- 49) 1177 (+/- 32)
> >>>>> async resume 2692 (+/- 326) 3556 (+/- 33)
> >>>>>
> >>>>> async+one-liner suspend 1600 (+/- 39) 1212 (+/- 41)
> >>>>> async+one-liner resume 2692 (+/- 324) 3579 (+/- 24)
> >>>>>
> >>>>> async+extra suspend 1496 (+/- 37) 1217 (+/- 38)
> >>>>> async+extra resume 1859 (+/- 114) 1923 (+/- 35)
> >>>>>
> >>>>> So, in my opinion, with the above set of "async" devices, it
> >>>>> doesn't
> >>>>> make sense to do async suspend at all, because the sync suspend
> >>>>> is actually
> >>>>> the fastest on both machines.
> >>>>
> >>>> I think the async suspend is not asynchronous enough then - what
> >>>> kind of
> >>>> time do you get if you simply comment out call to psmouse_reset()
> >>>> in
> >>>> drivers/input/mouse/psmouse-base.c:psmouse_cleanup()? (Just for
> >>>> testing
> >>>> purposes only, I don't think we want to do that by default.)
> >>>
> >>> The problem apparently is that the i8042 suspend/resume is
> >>> synchronous.
> >>>
> >>> Do you think it's safe to mark it as asynchronous?
> >>>
> >>
> >> Umm.. there lie dragons. There is an implicit relationship between
> >> i8042
> >> and PNP/ACPI devices representing keyboard and mouse ports, and I
> >> am not
> >> sure how happy i8042 (and most importantly the BIOS) will be if
> >> they get
> >> shut down before i8042. Also there is EC which is in theory
> >> independent
> >> but in practice not so much.
> >
> > I see.
> >
> > Is this possible to identify ACPI devices that should wait for the
> > i8042
> > suspend and that should be waited for by it on resume?
>
> We could try to add some dependencies while discovering PNP to get KBC
> addresses in i8042 but we need tomake sure we do it even in presence
> of i8042.nopnp.

Well, I guess this is the example of the off-tree dependencies that actually
matter Linus wanted. :-)

I guess there are quite a few devices that can depend on the i8042 in
principle, is this correct?

Rafael