Re: [patch] SCHED_SOFTRR starve-free linux scheduling policy ...

[Davide Libenzi]

On Mon, 14 Jul 2003, Mike Galbraith wrote:

> At 02:51 PM 7/13/2003 -0700, Davide Libenzi wrote:
>
> >This should (hopefully) avoid other tasks starvation exploits :
> >
> >http://www.xmailserver.org/linux-patches/softrr.html
>
> Yes, that ~works.  I couldn't starve root to death as a SCHED_SOFTRR user,
> but the system was very sluggish, with keystrokes taking uncomfortably
> long.  I also had some sound skips due to inheritance.  If I activate
> xmms's gl visualization under load, it inherits SCHED_SOFTRR, says "oink"
> in a very deep voice, and other xmms threads expire.  Maybe tasks shouldn't
> inherit SCHED_SOFTRR?

You might want to increase the K_something from 4 (25% CPU time) to a
lower value. Also, SOFTRR tasks should get a lower timeslice while they're
currently getting the RR one. The SOFTRR policy should be used by MM apps
in a way that the thread that uses it does the minimum amount of work in
there. Like the thing we do with IRQ processing.

> While testing, I spotted something pretty strange.  It's not specific to
> SCHED_SOFTRR, SCHED_RR causes it too.  If I fire up xmms's gl visualization
> with either policy, X stops getting enough sleep credit to stay at a usable
> priority even when cpu usage is low.  Fully repeatable weirdness.  See
> attached top snapshots.

RT tasks are pretty powerfull and should not be used to run everything ;)
What I was seeking with this patch was 1) deterministic latency 2) stave
protection.

- Davide