Messages in this thread | | | From | Daniel Phillips <> | Subject | Re: Ingo Molnar and Con Kolivas 2.6 scheduler patches | Date | Thu, 7 Aug 2003 16:42:55 +0100 |
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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.)
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.
> In theory, the real benefit of SCHED_SOFTRR is that an attempt to switch to > it can fail with -EMYBRAINISMELTING up front, so you know when it won't > work at the start, rather than having it glitch halfway through the run.
Not as implemented. Anyway, from the user's point of view, that would be an unpleasant way for a sound player to fail. What we want is something more like a little red light that comes on (in the form of error statistics, say) any time a softrr process gets demoted. Granted, there may be situations where what you want is the right behavior, but it's (as you say) a separate issue of resource allocation.
Regards,
Daniel
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