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Date: Mon, 14 Jan 2002 06:48:53 -0700
From: yodaiken@fsmlabs.com
To: yodaiken@fsmlabs.com
Cc: Momchil Velikov <velco@fadata.bg>,
        Daniel Phillips <phillips@bonn-fries.net>,
        Arjan van de Ven <arjan@fenrus.demon.nl>,
        Roman Zippel <zippel@linux-m68k.org>, linux-kernel@vger.kernel.org
Subject: Re: [2.4.17/18pre] VM and swap - it's really unusable
Message-ID: <20020114064853.E22065@hq.fsmlabs.com>
In-Reply-To: <E16PZbb-0003i6-00@the-village.bc.nu> <3C41A545.A903F24C@linux-m68k.org> <20020113153602.GA19130@fenrus.demon.nl> <E16PzHb-00006g-00@starship.berlin> <20020113223438.A19324@hq.fsmlabs.com> <87bsfx9led.fsf@fadata.bg> <20020114064548.D22065@hq.fsmlabs.com>
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In-Reply-To: <20020114064548.D22065@hq.fsmlabs.com>; from yodaiken@fsmlabs.com on Mon, Jan 14, 2002 at 06:45:48AM -0700
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I forgot the line that says: "Oliver pointed out the immediate problem but .."

On Mon, Jan 14, 2002 at 06:45:48AM -0700, yodaiken@fsmlabs.com wrote:
> On Mon, Jan 14, 2002 at 02:17:46PM +0200, Momchil Velikov wrote:
> > >>>>> "yodaiken" == yodaiken  <yodaiken@fsmlabs.com> writes:
> > yodaiken> 	It's not even clear how preempt is supposed to interact with SCHED_FIFO.
> > 
> > How so ? The POSIX specification is not clear enough or it is not to be followed ?
> 
> POSIX makes no specification of how scheduling classes interact - unless something changed
> in the new version.
> 
> But more than that, the problem of preemption is much more complex when you have
> task that do not share the "goodness fade" with everything else. That is, given a
> set of SCHED_OTHER processes at time T0, it is reasonable to design the scheduler so
> that there is some D so that by time T0+D each process has become the highest priority
> and has received cpu up to either a complete time slice or a I/O block. Linux kind of
> has this property now, and I believe that making this more robust and easier to analyze
> is going to be an enormously important issue.  However, once you add SCHED_FIFO in the
> current scheme, this becomes more complex. And with preempt, you cannot even offer the
> assurance that once a process gets the cpu it will make _any_ advance at all.
> 
> 
> 
> -- 
> ---------------------------------------------------------
> Victor Yodaiken 
> Finite State Machine Labs: The RTLinux Company.
>  www.fsmlabs.com  www.rtlinux.com

-- 
---------------------------------------------------------
Victor Yodaiken 
Finite State Machine Labs: The RTLinux Company.
 www.fsmlabs.com  www.rtlinux.com

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