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    SubjectRe: [patch, 2.6.11-rc2] sched: RLIMIT_RT_CPU_RATIO feature
    At 03:01 AM 1/28/2005 -0600, Jack O'Quin wrote:
    >Ingo Molnar <mingo@elte.hu> writes:
    >
    > > * Jack O'Quin <joq@io.com> wrote:
    > >
    > >> > i'm wondering, couldnt Jackd solve this whole issue completely in
    > >> > user-space, via a simple setuid-root wrapper app that does nothing else
    > >> > but validates whether the user is in the 'jackd' group and then keeps a
    > >> > pipe open to to the real jackd process which it forks off, deprivileges
    > >> > and exec()s? Then unprivileged jackd could request RT-priority changes
    > >> > via that pipe in a straightforward way. Jack normally gets installed as
    > >> > root/admin anyway, so it's not like this couldnt be done.
    > >>
    > >> Perhaps.
    > >>
    > >> Until recently, that didn't work because of the longstanding rlimits
    > >> bug in mlockall(). For scheduling only, it might be possible.
    > >>
    > >> Of course, this violates your requirement that the user not be able to
    > >> lock up the CPU for DoS. The jackd watchdog is not perfect.
    > >
    > > there is a legitimate fear that if it's made "too easy" to acquire some
    > > sort of SCHED_FIFO priority, that an "arm's race" would begin between
    > > desktop apps, each trying to set themselves to SCHED_FIFO (or SCHED_ISO)
    > > and advising users to 'raise the limit if they see delays' - just to get
    > > snappier than the rest.
    > >
    > > thus after a couple of years we'd end up with lots of desktop apps
    > > running as SCHED_FIFO, and latency would go down the drain again.
    >
    >I wonder how Mac OS X and Windows deal with this priority escalation
    >problem? Is it real or only theoretical?

    WRT the Mac, I thought OS X was created to cure the ills of cooperative
    multi-tasking. (which the priority arms race reminds me of)

    -Mike

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