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

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Message-Id: <200912182343.29190.rjw@sisk.pl>
Date:	Fri, 18 Dec 2009 23:43:29 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Alan Stern <stern@...land.harvard.edu>,
	Zhang Rui <rui.zhang@...el.com>,
	LKML <linux-kernel@...r.kernel.org>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	pm list <linux-pm@...ts.linux-foundation.org>
Subject: Re: Async suspend-resume patch w/ completions (was: Re: Async suspend-resume patch w/ rwsems)

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?

Rafael
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