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    SubjectRe: AMIGA will use Linux, but Linux has several "multimedia-deficiencies"
    In <99071018080700.00820@linuxhost.localdomain> Benno Senoner (sbenno@gardena.net) wrote:
    > Hello,

    > I've just read that the next generation AMIGA will use Linux as the core OS,
    > instead of QNX. ( http://www.amiga.com/diary/executive/linux-e.html )

    > Amiga is a multimedia platform, and therefore needs realtime capatibilites.

    > Unfortunately actually Linux doesn't allow to play any realtime
    > (low-latency) mulimedia content (audio/video,etc.) in a reliable fashion
    > , during high system load, especially disk I/O.
    > I was very disappointed when I benchmarked a 130ms max scheduling latency of a
    > realtime scheduled audio process (playing from RAM) under high disk I/O load on
    > my PII400 + 16GB UDMA harddisk. (for infos see my latency benchmark page)
    > Even Win98 is able to get 17ms audio latency on my machine (during
    > heavy disk I/O) without many problems.


    > It's a bit disappointing that under Linux we get latencies which are
    > 50-100times the realistic (<5ms) latencies, we are FAR AWAY from the hardware
    > limits.

    > I was shocked when disabling DMA on my HD, my realtime process was
    > not rescheduled for *4000ms* = 4sec !
    > (a 100m sprinter is able to run 35m in the same time :-) )

    > Not only the audio layer is affected but many other subsystems too.
    > For example benchmarking usleep() I noticed a max 100-150ms scheduling
    > latency during high disk I/O load.
    > I don't understand why a process should block occasionally up to 150ms , when
    > usleep()ing only a few ms, because of the high disk I/O.

    > Actually there seems not a big interest to cure these deficiencies, just
    > because many see Linux as a server OS , and not a desktop OS,
    > on a web-server or fileserver you don't need guaranteed timing.
    > (Or is there already some unoffical work underway to cure the scheduling
    > problems of Linux ?)

    > Who cares if his webpage shows up 150ms earlier or later ? ,
    > or if your netscape executable which comes from the NFS server, is loaded
    > 150ms later ? No one, I think.

    > Does anyone know if the disk device driver (or device drivers in general) can be
    > preempted from regular processes or is there no way to do this on Linux.
    > Do we really need a microkernel to handle realtime multimedia ?

    > Hopefully Amiga Inc, will help us to optimize these Linux deficiencies, through
    > collaborating with the kernel/audio/video developement folks.

    > comments ?

    Are you tested all this stuff with `hdparm -u 1' or not ? If not then it
    can be expected. Plus you can always use RTLinux if you wish ...




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