pretty much the only criticism of the RT-CPU patch was that the global sysctl is too rigid and that it doesnt allow privileged tasks to ignore the limit. I've uploaded a new RT-CPU-limit patch that solves this problem:
http://redhat.com/~mingo/rt-limit-patches/
i've removed the global sysctl and implemented a new rlimit, RT_CPU_RATIO: the maximum amount of CPU time RT tasks may use, in percent. For testing purposes it defaults to 80%.
the RT-limit being an rlimit makes it much more configurable: root tasks can have unlimited CPU time limit, while users could have a more conservative setting of say 30%. This also makes it per-process and runtime configurable as well. The scheduler will instantly act upon any new RT_CPU_RATIO rlimit.
(this approach is fundamentally different from the previous patch that made the "maximum RT-priority available to an unprivileged task" value an rlimit - with priorities being an rlimit we still havent made RT priorities safe against deadlocks.)
multiple tasks can have different rlimits as well, and the scheduler
interprets it the following way: it maintains a per-CPU "RT CPU use"
load-average value and compares it against the per-task rlimit. If e.g. the task says "i'm in the 60% range" and the current average is 70%,
then the scheduler delays this RT task - if the next task has an 80%
rlimit then it will be allowed to run. This logic is straightforward and
can be used as a further control mechanism against runaway highprio RT
tasks.
Very nice. I like the way this approach is evolving.
Cheers, Con
signature.asc
Description: OpenPGP digital signature
