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    SubjectRe: [patch] Real-Time Preemption, -RT-2.6.10-rc2-mm2-V0.7.30-2

    * Eran Mann <emann@mrv.com> wrote:

    > >>I´m seeing latencies of up to ~2000 microseconds. see attached traces
    > >>file for a small sample. I think I´m missing something obvious
    > >>config-wise but I don´t know what...
    > ...
    >
    > >this seems to imply IDE DMA related hardware overhead. Apparently what
    > >happens is that with certain motherboards/chipsets, if IDE DMA happens
    > >then that DMA transfer _completely locks up_ the system bus. Nothing
    > >happens, and the CPU is stalled in essence until the end of the DMA
    > >request.

    > Right on.
    > After hdparm -d0 I see maximum latency of 35 us after a full kernel
    > build with a few GUI apps in the background. I´ll try to find a
    > reasonable compromise.

    it might make sense to report this to the hw vendor as well, as these
    latencies dont occur at _every_ IDE DMA, it might be some sort of
    chipset (or BIOS) bug they might want to see resolved as well (if this
    isnt a ship-and-forget vendor). 2 msec stalls are not nice to a fair
    number of applications.

    Ingo
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