On 5/26/06, Wolfgang Woehl <tito@xxxxxxxxxx> wrote:
Wednesday 24 May 2006 17:24, Jack O'Quin: > The required components are now available, and are being provided > by a few leading-edge distributions. Had you installed Ubuntu Dapper > Drake (which is not yet officially released), you would not have seen > any problem. They chose to include the PAM patches and authorize > all users to start realtime threads be default. That is a reasonable > choice for them (given their goals), but would not be appropriate for > most other distributions. I thought a realtime-scheduling kernel gives well-defined portions of time and system resources to processes. Why does that mean userland could dos the kernel? Is there no kernel watchdog that would kick out processes with excessive demands? Does the kernel not keep a book for it's own needs?
Some do. What we all use in the Linux world is basically POSIX threads with fixed SCHED_FIFO priorities. These cannot be preempted by normal SCHED_OTHER user processes. Going into a loop with realtime priority, effectively locks out all other user processes. The kernel can still run, but not much else. Watchdog threads are typically provided by jackd or other mechanism, but are not built into the kernel. -- joq
