lkml.org 
[lkml]   [2003]   [Aug]   [7]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: Ingo Molnar and Con Kolivas 2.6 scheduler patches
Rob Landley wrote:
[...]
>
> Thinking out loud for a bit, please tell me if I'm wrong about SCHED_SOFTRR...
>
> Whatever the policy is, there's only so many ticks to go around and there is
> an overload for which it will fail. No resource allocation scheme can
> prevent starvation if there simply isn't enough of the resource to go around.
>
> So, how does SCHED_SOFTRR fail? Theoretically there is a minimum timeslice
> you can hand out, yes? And an upper bound on scheduling latency. So
> logically, there is some maximum number "N" of SCHED_SOFTRR tasks running at
> once where you wind up round-robining with minimal timeslices and the system
> is saturated. At N+1, you fall over. (And in reality, there are interrupts
> and kernel threads and other things going on that get kind of cramped
> somewhere below N.)


I don't know how this particular scheduler fail, but the problem
exists for any real-time system. Nobody can run "N+1" guaranteed
low-latency
tasks where N is the max, that is obvious.

A generic os scheduler can run almost any amount of tasks, with latencies
proportional to the amount of tasks.

A good RT scheduler won't even _try_ to run "N+1" RT tasks. The
last task will either fail to start, or fail the attempt to
increase its priority into RT. You may then kill (or un-prioritize)
some other RT task and try again.

Helge Hafting

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-03-22 13:47    [W:0.422 / U:2.968 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site