Re: SD still better than CFS for 3d ?(was Re: 2.6.23-rc1)

[Kasper Sandberg <lkml@metanurb.dk>]

On Sun, 2007-07-29 at 19:06 +0200, Ingo Molnar wrote:
> * Kasper Sandberg <lkml@metanurb.dk> wrote:
> 
> > Im still not so keen about this, Ingo never did get CFS to match SD in 
> > smoothness for 3d applications, where my test subjects are quake(s), 
> > world of warcraft via wine, unreal tournament 2004. [...]
> 
> here's an update: checking whether Wine could be a factor in your 
> problem i just tested latest CFS against latest SD with a 3D game 
> running under Wine: v2.6.22-ck1 versus v2.6.22-cfsv19 (to get the
> most comparable kernel), using Quake 3 Arena Demo under Wine (0.9.41). 
> Here are the results in a pretty graph:
> 
>    http://people.redhat.com/mingo/misc/cfs-vs-sd-wine-quake.jpg
> 
> or, in text:
> 
>          2.6.22-ck1                         2.6.22-cfs-v19
>    ------------------------            ------------------------
>    quake + 0 loops | 41 fps            quake + 0 loops | 41 fps
>    quake + 1 loop  |  3 fps            quake + 1 loop  | 41 fps
>    quake + 2 loops |  2 fps            quake + 2 loops | 32 fps
>    quake + 3 loops |  1 fps            quake + 3 loops | 24 fps
>    quake + 4 loops |  0 fps            quake + 4 loops | 20 fps
>    quake + 5 loops |  0 fps            quake + 5 loops | 16 fps
> 
> Quake3-under-Wine behavior under SD/-ck: framerate breaks down massively 
> during any kind of load. The game is completely unusable with 1 CPU loop 
> running already!

I run quake3 natively, ut2k4 natively, and world of warcraft under wine.

> 
> Quake3-under-Wine behavior under CFS: framerate goes down gently with 
> load, gameplay remains smooth. Framerate is still pretty acceptable and 
> the game is playable even with a 500% CPU overload. The graph looks good 
> and the framerate reduction goes roughly along the expected 1/n 
> 'fairness curve' - so it all looks pretty healthy. [Note: quake3 keeps 
> its fully 41 fps even with 1 competing loop running on the CPU due to 
> "sleeper fairness".]
> 
> [ i've re-tested this using other SD and ck versions and other CFS 
>   versions such as v2.6.23-rc1 and the results are the same. To get the 
>   fps result i started a simple game scene: Single Player /
>   Q3DM1 / I Can Win, turned on the fps display of Quake3, and did not 
>   move the player at all, just looked at the framerate that is 
>   displayed. (i also tried other scenes and other gameplay sections and 
>   they all behave consistently with the above results.) The system was
>   otherwise completely idle. While i trust these numbers take them with 
>   a grain of salt, i'm obviously not neutral in this thing :-) ]
> 
> so Kasper, i'll definitely need your help in tracking down your 3D 
> smoothness problem under CFS. I have the feeling that it could be some 
> odd factor that only hits your system, and once we've tracked that down 
> there will be a simple solution that does not affect the totality of the 
> scheduler. So far only you have reported any 3D game smoothness problem 
> against recent CFS versions. (all 3D feedback has been positive, and 
> that includes a number of gamers as well. Most of the 3D smoothness 
> problems were fixed in CFS v13..v15 and it has not been reported to have 
> regressed since then.)

I believe the responsibility for my situation is both IO and cpu load. i
dont know why SD does this. my test is to make spamasassin process mails
while i have these applications running(and wine is most sensitive, the
difference is almost negligable in the native applications, but very
much noticable with wine+wow)

could perhaps be filesystem related, i have my maildir(extremely large)
on reiserfs, and /home on xfs. what my mail client will do is download
mail, spamasassin it(loading database from home), then it will put to
imap server placing it on reiserfs, and then a "local" copy in my home.

while i only see the spamasassin thread as hogging cpu, i suspect IO is
also to blame.

> 
> 	Ingo