Date: Tue, 8 Jul 2003 00:48:36 -0700 (PDT)
From: Davide Libenzi <davidel@xmailserver.org>
To: Daniel Phillips <phillips@arcor.de>
cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: 2.5.74-mm1
In-Reply-To: <200307080307.18018.phillips@arcor.de>
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 <200307080307.18018.phillips@arcor.de>
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On Tue, 8 Jul 2003, Daniel Phillips wrote:

> 1. 400ms buffers are hated by users, as was noted previously.  They are
> passable for some applications, but way too laggy for others.
>
> 2. Even if you are will to have a 400-500 ms buffer, if you can prove that you
> will always meet that deadline, then it's a realtime system.
>
> 3. If you can show logically that you will nearly always meet the deadline,
> it's a soft realtime system.  That's what we're after here.  From a design
> standpoint, there are elegant soft realtime systems, and there are sucky
> ones.
>
> 4. So how do you propose to "program timings" so that it's really hard to miss
> those deadlines?

Having a backup of 400-500ms gives you an average hang-over of 200-250ms
that are hardly noticeable by a human in this topic. The issue is not if
you always meet the deadline, the issue is what amount of load will make
you miss it. If I have to hire five ppl clicking and dragging on my desktop
to make my player to skip, and it skips, I don't care if it missed the
deadline. This because my desktop will hardly see that load. But if you
have a 50-100ms backup, things turns out to be a little bit different.
If you pretend to run a `make -jUNREAL` and still have the audio not
skipping it is simply wrong. Running a `make -j20` in my machine shows an
average of 24 TASK_RUNNING tasks, that even if they're granted with a mere
40ms timeslice, it'll take a full second before an expired task will see
the light again. BTW, under such load RealPlayer skips badly, but I don't
really care since it never did while I was doing all the normal (and many
extra) stuff I'm doing on my desktop.


- Davide

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