SCHED_IDLE is not meant to (and cannot) be used as an administrative
restriction. It is only a way to tell the system "this process isn't
essential, don't run this unless you have some cputime to waste".
Ie the fact that the process can trick the system into scheduling it
like a normal process is uninteresting. It could just set its scheduling
policy to SCHED_OTHER if it wanted (you could prevent that, but allowing
a normal user to un-idle his own process is a _feature_).
IOW SCHED_IDLE is for cpu-bound processes (like raytracers, numeric
computations, compression etc); an io-bound process is not a good
candidate for SCHED_IDLE (you would have to also somehow restrict
the io-bw it can use, as that could have worse effects on the system
than the few % of cputime).
I'll look into the bonnie #s; but were I to guess it's lmbench
doing a _lot_ of syscalls - the patch i posted didn't penalize
the idle process for doing that (even though both the original
(unpublished) patch, and my current one does - i removed this,
and later added it back). I'll see if it still is a problem, and
if yes will try to find a reasonable compromise [==penalty :)].
Thanks for the numbers (these were for UP, right?).
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