Subject: Re: [PATCH] Staircase scheduler v7.4
From: Felipe Alfaro Solana <felipe_alfaro@linuxmail.org>
To: Con Kolivas <kernel@kolivas.org>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>,
       linux kernel mailing list <linux-kernel@vger.kernel.org>,
       Willy Tarreau <willy@w.ods.org>
In-Reply-To: <40E00AEA.4050709@kolivas.org>
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Date: Mon, 28 Jun 2004 19:11:45 +0200
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On Mon, 2004-06-28 at 22:11 +1000, Con Kolivas wrote:

> The design of staircase would make renicing normal interactive things
> - -ve values bad for the latency of other nice 0 tasks s is not
> recommended for X or games etc. Initial scheduling latency is very
> dependent on nice value in staircase. If you set a cpu hog to nice -5 it
> will hurt audio at nice 0 and so on. Nicing latency unimportant things
> with +ve values is more useful with this design. If you run X and
> evolution at the same nice value they will get equal cpu share for
> example so moving windows means redrawing evolution and X moving get
> equal cpu. Nicing evolution +ve will make X smoother compared to
> evolution redrawing and so on...

OK, just a few thoughts...

1. Both -mm3 and -np2 suffer from delays when redrawing "damaged"
windows (windows which were covered and now are being exposed): while
moving heavily a window over the screen, "damaged" windows are not
redrawn. I would say this is a sign of starvation. However, this does
not happen with -ck3 that is able to redraw "damaged' windows even while
heavily moving a window all over the screen.

I can see this by looking at some icons that are lying on my desktop.
With -mm3 and -np2, they are hardly redrawn while heavily moving a
window all around. With -ck3, I can see the icons and their respective
labels all the time.

2. Both -mm3 and -np2 show a very smooth behavior when moving windows
all around the screen. However, -ck3 is somewhat a little bit jerky. I
think this is a consequence of point number 1.

3. Both -mm3 and -ck3 are inmune to CPU hogs when mantaining
interactivity: running "while true; do a=2; done" doesn't seem to affect
the interactive behavior of them. I check this by running this CPU hog
and hovering my mouse over KXDocker, which is a nice applet for KDE
similar to the Mac OS X docker. KXDocker is another CPU hog by itself,
but plays nicely with the "while true" loop. However, -np2 seems to
suffer a little bit from starvation, as KXDocker animations don't feel
smooth.

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