Messages in this thread | | | Date | Fri, 28 Jan 2005 09:40:49 +0100 | From | Ingo Molnar <> | Subject | Re: [patch, 2.6.11-rc2] sched: RLIMIT_RT_CPU_RATIO feature |
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* 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.
(yeah, this feels like going back to the drawing board.)
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