Re: Ingo Molnar and Con Kolivas 2.6 scheduler patches

[William Lee Irwin III <wli@holomorphy.com>]

On Wednesday 06 August 2003 22:28, Rob Landley wrote:
>> So, how does SCHED_SOFTRR fail?  Theoretically there is a minimum timeslice
>> you can hand out, yes?  And an upper bound on scheduling latency.  So
>> logically, there is some maximum number "N" of SCHED_SOFTRR tasks running
>> at once where you wind up round-robining with minimal timeslices and the
>> system is saturated.  At N+1, you fall over.  (And in reality, there are
>> interrupts and kernel threads and other things going on that get kind of
>> cramped somewhere below N.)

On Thu, Aug 07, 2003 at 04:42:55PM +0100, Daniel Phillips wrote:
> The upper bound for softrr realtime scheduling isn't based on number
> of tasks, it's a global slice of cpu time: so long as the sum of
> running times of all softrr tasks in the system lies below limit,
> softrr tasks will be scheduled as SCHED_RR, otherwise they will be
> SCHED_NORMAL.

You're thinking of Little's law, which is describes the mean number of
waiters on a queue as the mean service time divided by the number of
servers times the mean inter-arrival time.


-- wli