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

[Rafael J. Wysocki]

On Wednesday 16 December 2009, Linus Torvalds wrote:
> 
> On Wed, 16 Dec 2009, Rafael J. Wysocki wrote:
> > 
> > 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.
> 
> Hmm. I certainly agree - your numbers do not seem to support any async at 
> all.
> 
> However, I do note that for the "extra patch" makes a big difference at 
> resume time. That implies that the resume serializes on some slow device 
> that wasn't marked async - and starting the async ones early avoids that. 
> 
> But without the per-device timings, it's hard to even guess what device 
> that was.
> 
> But even that doesn't really help the suspend cases, only resume.
> 
> Do you have any sample timing output with devices listed?

I'm going to generate one shortly.

Rafael
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