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    SubjectRe: 2.6.13 brings buffer underruns when recording DVDs in 16x (was Re: "Read my lips: no more merges" - aka Linux 2.6.14-rc1)
    Mathieu Fluhr <mfluhr@nero.com> wrote:
    >
    > According to the MMC documentation, you can thoeriticaly send at most
    > 65535 (16 bits int) blocks in one WRITE(10) CDB. This would means
    > sending a buffer of ~127 MB on case of writing a mode 1 data track (2048
    > bytes per block)...
    >
    > Now, practically, it is really not safe to send more than 64 KB per CDB
    > (Mostly device related). And with such values, you have the following:
    > - at 100 Hz -> 64 KB * 100 = 6400 KB/s <=> ~4.62x DVD
    > - at 250 Hz -> 64 KB * 250 = 16000 KB/s <=> ~11.55x DVD
    > - at 1000 Hz -> 64 KB * 1000 = 64000 KB/s <=> ~46.20x DVD

    But that implies that there's some piece of code somewhere (could be
    userspace, could be kernel) which is doing a timer-based sleep() in between
    each CDB. It shouldn't do that - it should be using the disk
    controller's completion interrupt for synchronisation.

    What userspace application are you using to write the DVDs, and is it
    possible to test a different one?

    -
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