ppc32: Weird process scheduling behaviour with 2.6.24-rc

[Michel Dänzer]

On Fri, 2008-01-18 at 13:34 +0100, Michel Dänzer wrote:
> This is on a PowerBook5,8.
> 
> In a nutshell, things seem more sluggish in general than with 2.6.23.
> But in particular, processes running at nice levels >0 can get most of
> the CPU cycles available, slowing down processes running at nice level
> 0.

The canonical test case I've come up with is to run an infinite loop
with

sudo -u nobody nice -n 19 sh -c 'while true; do true; done'

This makes my X session (X server running at nice level -1, clients at
0) unusably sluggish (it can even take several seconds to process ctrl-c
to interrupt the infinite loop) with 2.6.24-rc but works as expected
with 2.6.23.

Anybody else seeing this?


> I've seen this since .24-rc5 (the first .24-rc I tried), and it's still
> there with -rc8. I'd be surprised if this kind of behaviour remained
> unfixed for that long if it affected x86, so  I presume it's powerpc
> specific.

Or maybe not... I've bisected this down to the scheduler changes between
df3d80f5a5c74168be42788364d13cf6c83c7b9c/23fd50450a34f2558070ceabb0bfebc1c9604af5 and b5869ce7f68b233ceb81465a7644be0d9a5f3dbb . I'll try and bisect it further, but this is my main work machine, so I can't reboot it too often. I'm CC'ing Ingo in case he has any ideas offhand.


-- 
Earthling Michel Dänzer           |          http://tungstengraphics.com
Libre software enthusiast         |          Debian, X and DRI developer