Messages in this thread | | | Subject | Re: [patch, 2.6.11-rc2] sched: RLIMIT_RT_CPU_RATIO feature | From | "Jack O'Quin" <> | Date | Fri, 28 Jan 2005 03:01:28 -0600 |
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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? -- joq - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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