Re: SCHED_RR/SCHED_FIFO and kernel threads?

From: Patrik Hägglund
Date: Tue Jun 21 2005 - 18:42:20 EST

Well, Ingo's patch didn't made any difference for my problem with kernel starvation.

As expected, the workaround of raising the priority of the 'events' kernel thread made it possible to switch VT or switch windows in X (as described in my first mail), when running a simple infinite loop. When running arbitrary programs, I expect that all kernel threads needs higher priority.

I guess that the point with kernel threads is to push heavy kernel requests "backwards in the queue", thereby lowering the mean latency for SHED_OTHER processes. Therefore, using high priorities for kernel threads was not an option. However, this comes at the price of breaking SCHED_FIFO/SCHED_RR.

The only clean solution is probably to have priorities that are reserved for kernel threads. I saw that kernel threads in LynxOS may use a priority of 1/2 above of the user-space tasks it serves. This seems like a good solution to the problem.

Any other patches out there, ready for a test?

/Patrik Hägglund
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