Re: SCHED_RR is broken + patch

Artur Skawina (skawina@geocities.com)
Thu, 27 Apr 2000 02:27:21 +0200

Dimitris Michailidis wrote:
>
> And that, in turn, is because the counter for SCHED_FIFO processes is
> allowed to reach 0 and then it stays there causing a trip to the scheduler
> at every tick. Ideally, counter should be ingored for SCHED_FIFO, but that
> would require special case code in the timer interrupt. In my scheduler
> patch I set SCHED_FIFO counters to LONG_MAX, which effectively gives them an
> infinite slice.

last time i looked at the timer interrupt overhead it was so big that
the extra check+branch wouldn't make any significant difference.
the extra scheduler invocations did show up though.

In general, for real time the only thing that counts is worst case;
loosing a bit of performance isn't a problem, having some latency
peaks might be. Esp. ones that occur very rarely; ie won't happen
during testing, but show up several weeks later... No, it probably
doesn't matter in this case, but still, i'm not sure postponing the
bug by a few weeks is an improvment :)

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