[Caml-list] Scheduling thread problem kernel 2.6

[Christophe Raffalli <raffalli@univ-savoie.fr>]

Message posted to comp.os.linux.misc and caml-list.

I am having a scheduling problem with a Caml program that uses two threads:
- one CPU intensive thread
- one interface thread (using Glut + OpenGL) and often doing nothing

The problem is that the CPU intensive thread never gets more than 50% 
(near 100% expected) of the CPU (usually 20 to 30%). Moreover the thread 
only get less than 20% (near 50% expected) if another CPU intensive 
process is running.

I suspect that the scheduling algorithm uses the behaviour of the 
interface thread to predict (wrongly) that both threads need little CPU. 
This seems confirmed by the fact that call to Thread.yield in the 
interface thread slow down the CPU intensive thread !

The problem exists with all versions of kernel 2.6 I tried (from 2.6.3 
to 2.6.5 unpatched and the Mandrake 2.6.3). Everything is fine with a 
kernel 2.4.

Playing with SCHEDULING_SCOPE_SYSTEM and SCHEDULING_SCOPE_PROCESS 
changes nothing.

Any hint ?



-- 
Christophe Raffalli
Université de Savoie
Batiment Le Chablais, bureau 21
73376 Le Bourget-du-Lac Cedex

tél: (33) 4 79 75 81 03
fax: (33) 4 79 75 87 42
mail: Christophe.Raffalli@univ-savoie.fr
www: http://www.lama.univ-savoie.fr/~RAFFALLI
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