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SubjectRe: RT task scheduling
On Wed, Apr 05, 2006 at 08:25:04PM -0700, Darren Hart wrote:
> Part of the issue here is to define what we consider "correct behavior" for
> SCHED_FIFO realtime tasks. Do we (A) need to strive for "strict realtime
> priority scheduling" where the NR_CPUS highest priority runnable SCHED_FIFO
> tasks are _always_ running? Or do we (B) take the best effort approach with
> an upper limit RT priority imbalances, where an imbalance may occur (say at
> wakeup or exit) but will be remedied within 1 tick. The smpnice patches
> improve load balancing, but don't provide (A).

I regret getting into this discussion late, but it should always be (A)
if you're building a kernel for strict RT usage. (B) is for a system that's
more general purpose. It's not a "one policy fits all" kind of problem.

The search costs of (A) could be be significant and may degrade system
performance. Optimizations for that case is for another discussion.


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