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    SubjectRe: ehci-hcd affects hda speed
    On 15-04-08 21:56, Lev A. Melnikovsky wrote:

    > Sorry, I had virtually no time to answer earlier. If (hopefully) someone
    > is still interested, here's my feedback

    Interested yes, although being no longer in posession of the hardware it's a
    somewhat academic interest...

    > I have repeated experiments with P3B-F and VT6212L combination (to
    > improve visibility the AsyncSchedSleepTime is set to 1us):
    >
    > #0. Nothing is connected to USB, no ehci-hcd loaded
    > hda throughput 28+-1MB/s
    >
    > #1. ehci-hcd loaded, still no USB peripherals
    > hda throughput 28+-1 MB/s
    >
    > #2. Something (USB hub and FLASH drive tested) is attached
    > hda throughput 15+-1 MB/s
    >
    > #3. All USB peripherals are removed
    > hda throughput 15+-1 MB/s
    >
    > #4. ehci-hcd is rmmod'ed
    > hda throughput 28+-1MB/s
    >
    > The oddest peculiarity for me is the hysteretic difference between #1 and
    > #3 states. I mean experimental data (hda throughput) depends not on the
    > state (hardware/loaded modules), but on the path we followed.

    On the chip having inited itself at least. Yes, your results match what I
    experienced.

    > Interestingly enough, sampling registers (via /sys) often shows Async bit
    > set of the status register in the state #3. It is always cleared in #1.
    > The async file is empty in both states. I wonder, how many degrees of
    > freedom does an empty schedule have? Does "empty" mean "has no incomplete
    > requests" or "has no requests at all"? Just guessing...

    Should leave this up to David, but as far as I'm aware "no at all".

    > RH> The sleep time wasn't the core problem, so I wonder of later VIA chips do
    > RH> still have the active async schedule problem...
    > I don't think this is purely VIA problem. I did not _try_ to install that
    > VT6212L card into newer motherboard, but my _feeling_ is that we see an
    > "incompatibility" between older PCI mobo chipsets and VIA USB controller.

    I very much doubt that. Can't really imagine an off-silicon reason the chip
    would keep scanning the async schedule. I'm also now using a NEC controller
    card in that same machine and it also shows no problems.

    > Actually, taking into account superior PCI bandwidth of modern PCs (if
    > compared with my old P3B-F motherboard) I am not sure we can perform a
    > clean reliable test without PCI bus analyzer.

    http://lkml.org/lkml/2005/5/30/259

    >
    > -l
    >



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