Messages in this thread | | | Date | Fri, 28 Jan 2005 10:51:41 +0100 | From | Mike Galbraith <> | Subject | Re: [patch, 2.6.11-rc2] sched: RLIMIT_RT_CPU_RATIO feature |
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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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