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

[Rafael J. Wysocki]

On Saturday 19 December 2009, Dmitry Torokhov wrote:
> On Dec 19, 2009, at 1:33 PM, "Rafael J. Wysocki" <rjw@xxxxxxx> 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
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