MTRRs not working in 2.6 linux kernels?
Simon Strandman
simon.strandman at telia.com
Mon Oct 4 07:40:26 PDT 2004
Check out this thread for a workaround:
http://www.rage3d.com/board/showthread.php?t=33736241&page=1&pp=30
> When I try to use the application tvtime under Xorg 6.8.1 with Linux
> kernel 2.6.7, I get very choppy framerates; tvtime indicates that it is
> only getting about 50 MB/s for blitting to the screen. With the same
> version of Xorg and Linux kernel 2.4.22, I get smooth play, and tvtime
> indicates that it gets about 150 MB/s for blitting to screen. I made
> sure DRI wasn't playing a role in this by rmmod'ing the agpgart module
> before starting X.
>
> Of note is the difference in /proc/mtrr between 2.6 and 2.4
> kernels:
>
> in 2.4, it contains only
>
> reg00: base=0x00000000 ( 0MB), size= 256MB: write-back, count=1
> reg01: base=0x0ff80000 ( 255MB), size= 512KB: uncachable, count=1
>
> while in 2.6 it contains
>
> reg00: base=0x00000000 ( 0MB), size= 256MB: write-back, count=1
> reg01: base=0x0ff80000 ( 255MB), size= 512KB: uncachable, count=1
> reg02: base=0xe8000000 (3712MB), size= 2MB: write-combining, count=1
>
> Lastly, in the X.org log when running a 2.6 kernel the following line is
> displayed:
>
> (WW) RADEON(0): Failed to set up write-combining range (0xe8000000,0x1000000)
>
> while under 2.4 the following line is displayed:
>
> (==) RADEON(0): Write-combining range (0xe8000000,0x1000000)
>
> I am running a P4 at 1.8 Ghz Laptop with an AGP 4x Radeon 7500 and 16 MB
> of VRAM; it has 256 MB of system memory, which makes the third line of
> /proc/mtrr in the 2.6 kernels look wrong to my untrained eyes.
>
> I just tried this on kernel 2.6.9-rc2 with the same results
> as 2.6.7 and saw that dmesg complained about some mtrr overlapping with
> something else; if this is important, I can report the exact message.
>
> Perhaps this is a kernel issue and should be posted to the kernel list?
> Any help would be appreciated.
>
> --Jonathan Thambidurai
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