From: Mike Galbraith <efault@gmx.de>
To: Daniel Phillips <phillips@arcor.de>
Cc: Davide Libenzi <davidel@xmailserver.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [patch] SCHED_SOFTRR starve-free linux scheduling policy ...
Date: Sun, 10 Aug 2003 08:41:18 +0200 [thread overview]
Message-ID: <5.2.1.1.2.20030810080748.019cb090@pop.gmx.net> (raw)
In-Reply-To: <200308100141.13074.phillips@arcor.de>
At 01:41 AM 8/10/2003 +0100, Daniel Phillips wrote:
>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.
No, _not_ so. How is the SCHED_NORMAL (didn't that used to be called
SCHED_OTHER?) task ever going to receive the cpu when a realtime task is
runnable given that 1. task selection is done via sched_find_first_bit(),
and 2. realtime queues reside at the top of the array?
> > 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.
See the definition of rt_task() in sched.c, and the comments in sched.h
beginning at line 266.
-Mike
next prev parent reply other threads:[~2003-08-10 6:37 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <Pine.LNX.4.55.0307131442470.15022@bigblue.dev.mcafeelabs.c om>
2003-07-14 7:11 ` [patch] SCHED_SOFTRR starve-free linux scheduling policy Mike Galbraith
2003-07-13 21:51 ` Davide Libenzi
2003-08-09 14:05 ` Daniel Phillips
2003-08-09 17:47 ` Mike Galbraith
2003-08-09 23:58 ` Daniel Phillips
2003-08-10 6:06 ` Mike Galbraith
2003-08-10 0:41 ` Daniel Phillips
2003-08-10 6:41 ` Mike Galbraith [this message]
2003-08-10 15:46 ` Daniel Phillips
2003-08-10 17:49 ` Mike Galbraith
2003-08-10 20:28 ` Daniel Phillips
2003-08-11 5:31 ` Mike Galbraith
2003-08-11 13:54 ` Takashi Iwai
2003-08-10 2:05 ` Roger Larsson
2003-08-10 5:43 ` Nick Piggin
2003-08-10 7:41 ` Mike Galbraith
2003-08-10 7:56 ` Nick Piggin
2003-08-10 8:18 ` Mike Galbraith
2003-08-10 9:19 ` jw schultz
2003-08-11 17:01 ` Roger Larsson
2003-08-11 17:25 ` Takashi Iwai
[not found] ` <200308100405.52858.roger.larsson@skelleftea.mail.telia.com >
2003-08-10 7:11 ` Mike Galbraith
2003-08-12 7:23 ` Rob Landley
2003-08-12 23:35 ` Pavel Machek
2003-08-13 6:26 ` Mike Galbraith
2003-08-13 9:41 ` Pavel Machek
2003-07-14 7:12 ` Davide Libenzi
2003-07-14 7:24 ` Jamie Lokier
2003-07-14 7:35 ` Davide Libenzi
2003-07-14 9:11 ` Mike Galbraith
[not found] ` <Pine.LNX.4.55.0307140004390.3435@bigblue.dev.mcafeelabs.co m>
2003-07-14 8:14 ` Mike Galbraith
2003-07-14 15:09 ` Davide Libenzi
[not found] ` <Pine.LNX.4.55.0307140805220.4371@bigblue.dev.mcafeelabs.co m>
2003-07-14 16:06 ` Mike Galbraith
2003-07-14 17:22 ` Davide Libenzi
[not found] ` <Pine.LNX.4.55.0307141015010.4828@bigblue.dev.mcafeelabs.co m>
2003-07-15 4:56 ` Mike Galbraith
2003-07-15 15:47 ` Davide Libenzi
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