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