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    SubjectRe: Ingo Molnar and Con Kolivas 2.6 scheduler patches
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    On Wed, Jul 30, 2003 at 09:46:41AM -0500, Daniel Phillips wrote:
    > On Tuesday 29 July 2003 08:56, Timothy Miller wrote:
    > > ...since we're dealing with real-time and audio issues, is there any
    > > way we can do this: When the interrupt arrives from the sound card so
    > > that the driver needs to set up DMA for the next block or whatever it
    > > does, move any processes which talk to an audio device to the head of
    > > the process queue?
    >
    > That would be a good thing. To clarify, there are typically two buffers
    > involved:
    >
    > - A short DMA buffer
    > - A longer buffer into which the audio process generates samples
    >
    > There are several cycles through the short buffer for each cycle through the
    > long buffer. On one of these cycles, the contents of the long buffer will
    > drop below some threshold and the refill process should be scheduled,
    > according to your suggestion. Developing a sane API for that seems a little
    > challenging. Somebody should just hack this and demonstrate the benefit.
    >
    > In the meantime, the SCHED_SOFTRR proposal provides a way of closely
    > approximating the above behaviour without being intrusive or
    > application-specific.

    You might also like to think about driving the scheduler with an
    interrupt from the DMA device, if it's regular, or VBL (vertical
    retrace) for video/graphics applications. IRIX's REACT/pro RT system
    does stuff like this.

    http://techpubs.sgi.com/library/tpl/cgi-bin/getdoc.cgi?coll=0650&db=bks&srch=&fname=/SGI_Developer/REACT_PG/sgi_html/pr02.html

    It's in their frame scheduler section.

    bill

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