Messages in this thread | | | Date | Thu, 15 Jul 1999 13:36:02 +0200 | From | Sven Heursch <> | Subject | Re: SCHE_RR/FIFO |
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"Stephen C. Tweedie" wrote:
> 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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