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

    Rafael


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