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Old 08-09-08, 08:02 AM   #1
interzoneuk
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Default 2.6.26 kernel - x86 PAT support - should I enable it ?

Hi.

I have noticed that the 2.6.26 kernel has a new option

X86_PAT - from MTRR (in procesor)

I did try this option in a kernel compile buty it seemed to make (some games) really jerky ...

Should this option be enabled if using the NVIDIA drivers, I have latest drivers on Geforce 8500 - AMD64 machine - I use 32 and 64 bit distros.

Any advice would be appreciated

Cheers
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Old 08-09-08, 10:01 AM   #2
zander
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Default Re: 2.6.26 kernel - x86 PAT support - should I enable it ?

Provided you use a recent NVIDIA Linux graphics driver release, you can safely enable the option. If in doubt, leave it disabled for now.
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Old 08-11-08, 04:28 AM   #3
interzoneuk
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Default Re: 2.6.26 kernel - x86 PAT support - should I enable it ?

Hi.

I did try to compile with the option - again some games - most noticeably paintball2 become completely unplayable. (really really bad) .. However other games seemed faster (this could just be because it is a later kernel)......

I am using 173.14.12 for Linux x86-64 (latest driver)

Has anyone else had any joy / noticed issues with the option (and nvidia drivers) ?

Is there any bug report I can provide (in relation to the slow games) Or shall I just ignore it?

My fear it that Distros in the future may well have the option as default in the kernel - this may cause a flood of bug reports.....
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Old 08-11-08, 10:51 AM   #4
Dragoran
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Default Re: 2.6.26 kernel - x86 PAT support - should I enable it ?

I didn't notice any slowdown nor speedup with using 2.6.26 with X86_PAT enabled.
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Old 08-12-08, 12:47 AM   #5
energyman76b
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Default Re: 2.6.26 kernel - x86 PAT support - should I enable it ?

and even with PAT enabled in the kernel there is a big chance that PAT are disabled anyway. The whitelist of CPUs is pretty short.
[ 0.000000] x86 PAT enabled: cpu 0, old 0x7040600070406, new 0x7010600070106
[ 0.136657] x86 PAT enabled: cpu 1, old 0x7040600070406, new 0x7010600070106
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Old 08-12-08, 12:27 PM   #6
Dragoran
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Default Re: 2.6.26 kernel - x86 PAT support - should I enable it ?

it is enabled here
Quote:
x86 PAT enabled: cpu 0, old 0x7040600070406, new 0x7010600070106
x86 PAT enabled: cpu 1, old 0x7040600070406, new 0x7010600070106
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Old 08-12-08, 01:16 PM   #7
energyman76b
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Default Re: 2.6.26 kernel - x86 PAT support - should I enable it ?

sure that it doesn't get deactivated later? and that you didn't enable/disable other stuff?
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Old 08-13-08, 01:27 AM   #8
ocilent1
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Default Re: 2.6.26 kernel - x86 PAT support - should I enable it ?

Yes, I had to disable it for the kernels that I build as it was causing significant performance regressions when I was playing sauerbraten (it was stuttering so bad it became unplayable). Once X86_PAT under 2.6.26 was disabled, the performance was again comparable to when I was using the 2.6.25 kernels. I am using the latest stable nvidia driver release (173.14.12) along with a 6600gt and a AMD64 3500+ cpu.
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Old 08-13-08, 02:51 PM   #9
interzoneuk
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Default Re: 2.6.26 kernel - x86 PAT support - should I enable it ?

Hi - I am also running AMD64 - X2 4600

I have tried (with same results) with Opensuse 11 AMD64, gentoo AMD64 and Ubuntu (32bit) - with 2.6.26.2 kernel and 173.14.12.

Perhaps a AMD64 issue ?
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Old 08-13-08, 04:05 PM   #10
energyman76b
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Default Re: 2.6.26 kernel - x86 PAT support - should I enable it ?

I hadn't problems with my X2 6000 and a 8600GT with PAT enabled.

Maybe a distro or mobo or whatever issue?
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Old 08-13-08, 04:16 PM   #11
interzoneuk
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Default Re: 2.6.26 kernel - x86 PAT support - should I enable it ?

not a distro issue - same thing on 3 different ones...

have latest bios on

Gigabyte - AMD Socket AM2 - GA-M55S-S3
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Old 08-15-08, 04:36 AM   #12
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Default Re: 2.6.26 kernel - x86 PAT support - should I enable it ?

For those experiencing performance problems with x86_PAT enabled kernels and don't wish to recompile, you can always use the 'nopat' kernel boot option which will disable it. You'll end up with something like this in your dmesg output:

[ocilent1@localhost ~]$ dmesg |grep PAT
PAT support disabled.
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