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Old 08-17-08, 12:56 PM   #13
interzoneuk
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Default Re: 2.6.26 kernel - x86 PAT support - should I enable it ?

Thanks ocilent1 for the kernel line advice.

I shall give that a go

Cheers !
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Old 08-19-08, 04:17 AM   #14
tzp
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Exclamation Re: 2.6.26 kernel - x86 PAT support - should I enable it ?

I had also problems when enabling x86_PAT.

My machine is a dual core AMD Athlon x2 3600+, the GPU is a 8500 GT, the kernel is 2.6.26.2 with nvidia driver 173.14.12 (similar to interzoneuk's config).

I used glxgears to get a rough impression about the speed, and the difference was dramatic:
with PAT on: 2700 fps (with the cog wheels stopping for short periods sometimes)
with PAT off: 5900 fps.

I know, I know, glxgears is not a benchmark, but this huge difference should be an exclamation mark.

So I must disagree with zander's statement.
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Old 08-25-08, 05:48 AM   #15
ZicoTheTux
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Default Re: 2.6.26 kernel - x86 PAT support - should I enable it ?

Seems X86_PAT is directly responsible for this Problem:
http://www.nvnews.net/vbulletin/show...hlight=x86_pat

This at least explains why glxgears also has such low rates. After my observation it only affects OpenGL apps which are not very demanding in CPU/GPU usage.
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Old 08-25-08, 07:09 AM   #16
energyman76b
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Default Re: 2.6.26 kernel - x86 PAT support - should I enable it ?

similar observation with ATI.
PAT on = 3d ****. Constant stuttering
Pat off = 3d perfect.

Seems that PAT needs a lot maturing until it is usable.
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Old 08-25-08, 07:24 AM   #17
Fackamato
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Default Re: 2.6.26 kernel - x86 PAT support - should I enable it ?

What is PAT really, and what does it do, except cause trouble in gaming?
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Old 08-25-08, 07:32 AM   #18
energyman76b
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Default Re: 2.6.26 kernel - x86 PAT support - should I enable it ?

http://en.wikipedia.org/wiki/Page_Allocation_Table
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Old 08-25-08, 04:37 PM   #19
zander
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Default Re: 2.6.26 kernel - x86 PAT support - should I enable it ?

I tried to reproduce the performance problems reported with different Athlon systems (single/dual-core), kernels (2.6.26-git9, 2.6.26.3, x86 and x86-64, UP/SMP) and GPUs (NV43, G80, G92). In all of my tests, the performance results with and w/o the Linux kernel's PAT WB support were identical.

If you are experiencing the performance problem discussed in this thread, please generate and attach an nvidia-bug-report.log file, your kernel's configuration file and reproduction steps.
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Old 08-25-08, 05:25 PM   #20
kcrudup
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Default Re: 2.6.26 kernel - x86 PAT support - should I enable it ?

I have PAT enabled on my T9300 (2.5GHz) Core2Duo 64-bit and haven't seen any slowdowns either. I'm (currently) running 2.6.26.3 and have at times run the latest 2.6.27-git.
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Old 08-25-08, 05:52 PM   #21
xorbe
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Default Re: 2.6.26 kernel - x86 PAT support - should I enable it ?

I think x.org and kernel pat need to agree about what the pages are -- it probably doesn't have much to do with nv/ati driver. People should probably spec which version of x.org they've got. Kernel and x.org have to coordinate properly.
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Old 08-25-08, 06:05 PM   #22
zander
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Default Re: 2.6.26 kernel - x86 PAT support - should I enable it ?

@xorbe: which pages are you referring to? As far as any WB memory allocations and mappings known to the NVIDIA driver stack are concerned, X.Org has no direct control over the associated pages' mappings' attributes.
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Old 08-26-08, 04:39 AM   #23
storg
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Default Re: 2.6.26 kernel - x86 PAT support - should I enable it ?

Tried 2.6.26.3 (from kernel.org) on the weekend, all was fine until I tried to play Neverwinter Nights(1.68), terrible is the only comment I could have about performance.

Went back to 2.6.20.4, all ok.

Then I found this thread today, turned off PAT, and it works fine.

Here's a bug report, but its got # CONFIG_X86_PAT is not set, in the running kernel now.

reproduction steps, only thing I noticed crook, was NWN, the first menu you come to, is slow and jerky (the rest of it isn't good either).

Also if it matters, I fell back to gcc --version -> gcc-4.1 (GCC) 4.1.3 20070629 (prerelease) (Debian 4.1.2-13), the original problem kernel (with PAT on) was compiled with,
gcc 4.3 --version -> gcc-4.3 (Debian 4.3.1-2) 4.3.1, but since was a headache flipping back and forth(between kernels and gcc versions, my 2.6.20.4 was compiled with 4.1), I went back to 4.1
Attached Files
File Type: gz nvidia-bug-report.log.gz (30.9 KB, 105 views)
File Type: gz dot-config-2.6.26.3.gz (11.7 KB, 97 views)

Last edited by storg; 08-26-08 at 04:54 AM. Reason: forgot .config file
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Old 08-26-08, 04:51 AM   #24
ZicoTheTux
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Default Re: 2.6.26 kernel - x86 PAT support - should I enable it ?

Okay I generated a bug report.

It's easy to see the effect for me:
- glxgears drops a lot of performance with PAT enabled.
- Swapping in doublebuffer created a big delay (like posted in that thread I linked before).
I ALSO noticed these effects do NOT happen in a more demanding OpenGL application like Armagetron (which renders very fast) or Nexuiz (which uses many effects)

The problem also happens on different Desktops/WMs - so this is no KDE4 thing (just to be sure).

I somehow REALLY doubt this is actually a NVidia problem. I just htink PAT is not really okay already.

I also should say I am using a Dual Core CPU so probably PAT somehow screws up scheduling? I haven't digged so deep anymore, sorry.

Xorg Server: xorg-server 1.4.2-1

I think this is all I can say. As said I really doubt this is actually a driver bug or somewhat... but I can't say for sure. So I would be pleased if just the boot-option *nopat* would be somehow listed in the NVidia docs as like "try this once..."-hint.

Thank you.
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File Type: gz nvidia-bug-report.log.tar.gz (21.9 KB, 118 views)
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