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SubjectRe: [SCHED] wrong priority calc - SIMPLE test case
On Sun, 01 Jan 2006 00:44:10 +1100
Peter Williams <pwil3058@bigpond.net.au> wrote:

> OK. This probably means that the parameters that control the mechanism
> need tweaking.
>
> There should be a file /sys/cpusched/attrs/unacceptable_ia_latency which
> contains the latency (in nanoseconds) that the scheduler considers
> unacceptable for interactive programs. Try changing that value and see
> if things improve? Making it smaller should help but if you make it too
> small all the interactive tasks will end up with the same priority and
> this could cause them to get in each other's way.

I've tried different values and sometimes I've got a good feeling BUT
the behaviour is too strange to say something.

Sometimes I get what I want (dd priority ~17 and CPU eaters prio
25), sometimes I get a total disaster (dd priority 17 and CPU eaters
prio 15/16) and sometimes I get something like DD prio 22 and CPU
eaters 23/24.

All this is not well related to "unacceptable_ia_latency" values.

What I think is that the priority calculation in ingosched and other
schedulers is in general too weak, while in other schedulers is rock
solid (read: nicksched).

Maybe is just that the smarter a scheduler want to be, the more fragile
it will be.

--
Paolo Ornati
Linux 2.6.15-rc7-lial on x86_64
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