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Old 05-08-06, 12:07 PM   #1
marcin314
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Default Kernel 2.6 and OpenGL

I have noticed a very strange and annoying behaviour.
If I am using OpenGL and other program which uses a lot
of cpu then OpenGL apps slowing down to about 5 fps.

Simple Test
$ glxgears
$ nbench

Then glxgears fps drop from almost 1300 to 5 fps.

If I set __GL_SYNC_TO_VBLANK then everything is OK
glxgears has 75 fps (vertrefresh) even if CPU burns
But without __GL_SYNC_TO_VBLANK glxgears takes
a lot of sys time.
--- script cpuinfo ----
#!/bin/sh

delay=1
read cpu old_user old_nice old_sys old_idle rest </proc/stat
sleep $delay
while read cpu user nice sys idle rest </proc/stat; do
echo -en "\rUser:$((user-old_user)) Nice:$((nice-old_nice)) Sys:$((sys-old_sys)) Idle:$((idle-old_idle)) ";
let "old_user=user, old_nice=nice, old_sys=sys, old_idle=idle";
sleep $delay;
done
-----------------------

and then when I run nbench sys time drops and fps as well.

I have tried to rebuild the kernel couple of times with
different settings and it doesn't help either.

At this point I would like to know if this is hardware
problem or driver?

My specs:
Processor : AMD Athlon(TM) XP 2600+ Barton
Motherboard : ASUS A7V600
Kernel : 2.6.16.14 , 2.6.16-ck9
Graphics card : GeForce4 MX 440 AGP 8x NV18
Nvidia driver : 1.0.8756


Regards,
Marcin
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Old 05-08-06, 12:19 PM   #2
netllama
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Default Re: Kernel 2.6 and OpenGL

This is expected behavior, as glxgears is a cpu bound application. This is why glxgears is a poor benchmark tool.

Thanks,
Lonni
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Old 05-08-06, 12:43 PM   #3
marcin314
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Default Re: Kernel 2.6 and OpenGL

I agree with you but glxgears is only an example.
At first I have noticed this when I played Quake and
ran some apps in background (even "nice" priority).
I should also mention that under kernel 2.4 this is
much less noticeable.

Marcin
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Old 05-08-06, 01:15 PM   #4
Lithorus
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Default Re: Kernel 2.6 and OpenGL

Which scheduler did you use?
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Old 05-08-06, 01:31 PM   #5
marcin314
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Default Re: Kernel 2.6 and OpenGL

As a matter of fact I have tried almost every combination. At the moment
I'm using ck9 staircase scheduler with Anticipatory I/O but also tried CFQ
and Deadline. I think that this is some problem with either hardware or
driver because I got info that under an Intel i915 running nice -10 nbench
didn't slow down glxgears much at all.

Marcin
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Old 05-08-06, 03:38 PM   #6
Lithorus
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Default Re: Kernel 2.6 and OpenGL

Quote:
Originally Posted by marcin314
As a matter of fact I have tried almost every combination. At the moment
I'm using ck9 staircase scheduler with Anticipatory I/O but also tried CFQ
and Deadline. I think that this is some problem with either hardware or
driver because I got info that under an Intel i915 running nice -10 nbench
didn't slow down glxgears much at all.

Marcin
But that intel i915 system could just aswell be a dual-core/smp setup.
Also -10 will actually increase the priority of nbench.

Edit:
I tried it with both my ATI setup and Nvidia setup (both 2.6 kernels and latest drivers). Running nbench with a nice of -10 pretty much killed glxgears. With nice 10 it dropped to about 75% on both setups and with 19 perfomance stayed the same. Both setups were non-dualcore.

What you are seeing is the difference between 2.4 and 2.6 kernels way of interpreting the priority system. Some says that 2.6 is better at respecting them. Check this link out for more info :
http://www.cs.uh.edu/Preprints/prepr...H-CS-06-02.pdf (check page 6)

Last edited by Lithorus; 05-08-06 at 04:04 PM.
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Old 05-08-06, 04:04 PM   #7
marcin314
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Default Re: Kernel 2.6 and OpenGL

The intel i915 is in fact a laptop Pentium M 1.73 GHz.

I also notice that if I have tried
$ strace glxgears
and nbench then fps have increased to about 100!

If you are running script cpuinfo how much sys time takes glxgears?
In my case it is about 63% (kernel 2.6) and 30% (kernel 2.4)

BTW by nice -10 I meant nice -n 10
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Old 05-09-06, 07:59 AM   #8
Lithorus
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Default Re: Kernel 2.6 and OpenGL

User:60 Nice:31 Sys:8 Idle:0
kernel 2.6 with nice -n 10

User:87 Nice:4 Sys:9 Idle:0
with nice -n 19

(laptop AMD64 3000+)

Which distros are you testing on? And have you tested with a smp compiled kernel? I'm running Dapper on both my systems and with the distro provided kernels which is compiled for SMP by default.

Btw. everything is run on Xgl, not sure if it affects the results.

Last edited by Lithorus; 05-09-06 at 08:14 AM.
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Old 05-09-06, 09:13 AM   #9
marcin314
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Default Re: Kernel 2.6 and OpenGL

I recompiled kernel with SMP but it doesn't help either
In fact sys time is even higher (glxgears alone)

User:32 Nice:0 Sys:68 Idle:0
kernel 2.6 SMP

I'm using Gentoo with ck-sources (ck10 now) but as I mention
before I have tried vanilla-sources as well.

It seems that this is probably hardware issue maybe chipset VIA KT600
or my old GeForce 4. I have no idea.

Last edited by marcin314; 05-09-06 at 09:57 AM.
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Old 05-09-06, 11:42 AM   #10
Lithorus
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Default Re: Kernel 2.6 and OpenGL

Could you post a nvidia bug report? Perhaps you're not using the appropiate agp module (internal vs external agpgart). You could try with both.
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Old 05-09-06, 12:05 PM   #11
marcin314
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Default Re: Kernel 2.6 and OpenGL

I have already tried both NvAgp "1" and NvAgp "2" and
still sys time is very high about 65-70%
Attached Files
File Type: zip nvidia-bug-report.zip (22.8 KB, 114 views)
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Old 05-09-06, 02:21 PM   #12
Lithorus
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Default Re: Kernel 2.6 and OpenGL

When using nvagp "2" which agp modules are loaded? The best would ne to make a nvidia bug report with nvagp "2" also.

(not likely to be the problem, but worth a try anyway) :
It seems your secondary usb ports share irq with the graphics board, could you perhaps try and disable them in the bios?
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