lkml.org 
[lkml]   [2003]   [Aug]   [9]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: [patch] SCHED_SOFTRR starve-free linux scheduling policy ...
Date
On Saturday 09 August 2003 18:47, Mike Galbraith wrote:
> > But the patch has a much bigger problem: there is no way a SOFTRR task can
> > be realtime as long as higher priority non-realtime tasks can preempt it.
> > The new dynamic priority adjustment makes it certain that we will
> > regularly see normal tasks with priority elevated above so-called
> > realtime tasks. Even without dynamic priority adjustment, any higher
> > priority system task can unwttingly make a mockery of realtime schedules.
>
> Not so.

Yes so. A SCHED_NORMAL task with priority n can execute even when a
SCHED_FIFO/RR/SOFTRR task of priority n-1 is ready. In the case of FIFO and
RR we don't care because they're already unusable by normal users but in the
case of SOFTRR it defeats the intended realtime gaurantee.

> Dynamic priority adjustment will not put a SCHED_OTHER task above
> SCHED_RR, SCHED_FIFO or SCHED_SOFTRR, so they won't preempt.

Are you sure? I suppose that depends on the particular flavor of dynamic
priority adjustment. The last I saw, dynamic priority can adjust the task
priority by 5 up or down. If I'm wrong, please show me why and hopefully
point at specific code.

On the other hand, this doesn't really matter, because the first problem above
still exists, and causes the same result: attempted realtime scheduling that
isn't.

Regards,

Daniel


-
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:0.400 / U:0.144 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site