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    SubjectRe: [patch] voluntary-preempt-2.6.8.1-P0

    * Lee Revell <rlrevell@joe-job.com> wrote:

    > I believe the constant-time behavior that I reported was an artifact
    > of ALSA xrun debugging. Now it seems like the latency produced *does*
    > correspond directly to the amount of memory being mlockall'ed. If
    > ./mlockall-test 1500 triggers an xrun at all it's ~0.2ms. 3000
    > triggers a ~1ms xrun, and 10000 a ~3 ms xrun.

    ah ...

    could this be some DMA starvation effect? Or is this xrun calculated
    from arrival of the audio interrupt (hence DMA completion) to the actual
    running of jackd?

    > > could you try another thing: modify mlockall-test.cc to use mlock() on
    > > the freshly allocated anonymous pages? Does this produce the same
    > > latencies? mlockall() prefaults _all_ pages the process currently has.
    > > Maybe mlockall() touches some page that is mapped both by jackd and
    > > mlockall-test and thus somehow interacts with jackd's scheduling.
    >
    > I don't know C++, Florian wrote this program. Can you provide a
    > pseudo-patch?

    your above observation wrt. linearity of the xrun makes it less likely
    that the issue is caused by page sharing between jackd and
    mlockall-test. (if then they share a constant amount of pages.)

    but it would be nice to test it anyway, i've attached mlock-test.cc.

    Ingo
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