> Hi,
>
> On Wed, 14 Jul 1999 14:28:14 +0200, Sven Heursch
> <Sven.Heursch@unibw-muenchen.de> said:
>
> > Could it be that the scheduler in the kernel 2.2 has problems with the
> > priority based scheduling algorithm SCHED_FIFO and SCHED_RR. The
> > verification was made with two concurrent running processes with the
> > real time priorities 30 and 99. Normaly the higher one should be
> > scheduled first. But in Linux 2.2 that do not happend evereytime.
>
> What test case breaks the rule for you? The scheduler's goodness
> function should still absolutely prefer non-SCHED_OTHER processes.
Yes, indeed, the kernel source code says so! But the reality is different.
For example:
We have two processes, A & B. A has the priority 99, B the priority 30. Both
are the only processes which are scheduled with SCHED_FIFO in the system.
Process A starts and goes in nanosleep(). Now B got the CPU and does for
example the access() system call. After a few micorseconds, an interrupt is
generated and interrupts the process B. Process A has installed an
interrupthandler for that interrupt before and is beeing signaled by the
ISR.
Now the crazy thing: Wheather A has the highest priority in the system and
is now runnable, process B is being scheduled after the ISR in Kernel 2.2.
Process A is sleeping on.
I can generate the interuppt whenever I want, the same effect appears.
In Kernel 2.0 it works fine.
Any ideas?
greetings
S.Heursch
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