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    SubjectRe: Memory barrier needed with wake_up_process()?
    On Mon, 16 Jan 2017, Felipe Balbi wrote:

    > Sorry for the long delay, I finally have more information on this. All
    > this time I was doing something that I never considered to matter: I've
    > been running host and peripheral on the same machine. Now that I have
    > tracepoints on xHCI as well, I could see that these 30 seconds of
    > "nothing" is actuall full of xHCI activity and I can see that for the
    > duration of these 30 seconds preempt depth on the CPU that (eventually)
    > queues a request on dwc3, is always > 1 (sometimes 2, most of the time
    > 1). My conclusion from that is that xHCI (or usbcore ?!?) locks the CPU
    > and g_mass_storage is spinning for over 30 seconds at which point
    > storage.ko (host side class driver) dequeues the request.
    >
    > I'll see if I can capture a fresh trace with both xHCI and dwc3 with
    > this happening, but probably not today (testing stuff for -rc).

    Does anything change if the host and peripheral are separate machines?

    Alan Stern

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