Re: [gentoo-user] New motherboard, new CPU => MTRR problems

[J. Roeleveld]

On Wednesday, March 25, 2020 7:09:04 AM CET tuxic@××××××.de wrote:
> Hi,
>
> the hardware consists of:
> AMD Ryzen 5 3600
> MSI Tomahawk MAX
> 32GB RAM (Corsair Venegeance 2x16GB,dual channel)
> NVidia RTX 2060 SUPER
>
> cat /proc/mtrr gives me
>
> reg00: base=0x000000000 (    0MB), size= 2048MB, count=1: write-back
> reg01: base=0x080000000 ( 2048MB), size= 1024MB, count=1: write-back
> reg02: base=0x0c0000000 ( 3072MB), size=  512MB, count=1: write-back
> reg03: base=0x0dc0a0000 ( 3520MB), size=   64KB, count=1: uncachable
>
> -> there is a chunk of uncachable memory
>
> I activated the sanitizer in the kernel and in kernel I found
> this:
>
>
> [    0.000000] MTRR default type: uncachable
> [    0.000000] MTRR fixed ranges enabled:
> [    0.000000]   00000-9FFFF write-back
> [    0.000000]   A0000-BFFFF write-through
> [    0.000000]   C0000-FFFFF write-protect
> [    0.000000] MTRR variable ranges enabled:
> [    0.000000]   0 base 000000000000 mask FFFF80000000 write-back
> [    0.000000]   1 base 000080000000 mask FFFFC0000000 write-back
> [    0.000000]   2 base 0000C0000000 mask FFFFE0000000 write-back
> [    0.000000]   3 base 0000DC0A0000 mask FFFFFFFF0000 uncachable
> [    0.000000]   4 disabled
> [    0.000000]   5 disabled
> [    0.000000]   6 disabled
> [    0.000000]   7 disabled
> ...
> [    0.000000]  gran_size: 64K 	chunk_size: 64M 	num_reg: 4
lose cover
> RAM: 0G
>
> So I set the kernel cmdline to:
> BOOT_IMAGE=/vmlinuz-5051101-64-RT root=/dev/sda11 ro console=tty0
> console=ttyS0,115200n8 enable_mtrr_cleanup mtrr_spare_reg_nr=1
> mtrr_gran_size=64K mtrr_chunk_size=64M
>
> rebooted and found the same problem unchanged.
>
> The Gentoo docs says, that there is a BIOS setting - probably under
> "CPU" - which I should set from continuos to separated...but nowaday
> BIOSse may look like a part of a Science Fiction moview...but I can
> find those setting neither under "EZ" (for "easy settings" not under
> "advanced" (for "danger ahead - you may screw up your board").
>
> The bios of the board is not the top newest...it is the previous
> version.
> The changelog of the newest BIOS does not mention anything I would
> see as related to the mtrr problem...
>
> Background: The RTX 2060 SUPER was intended to replace the
> old GTX 960 I had....but the "BMW27" benchmark with Blender
> is slower than with the GTX 960...
>
> How can I fix the mtrr problem (and the performance problem
> of the graphics card, is related) ?
>
> Thanks a lot in advance for any help!
> Cheers!
> Meino

According to the following, MTRR is being phased out in favor of PAT:
https://www.kernel.org/doc/html/latest/x86/mtrr.html

Something that looks more promising:
https://forums.funtoo.org/topic/1865-properly-configuring-mtrr/

Sorry I can't help more, never looked into this myself, but will probably when 
I do manage to find the time.
If you figure it out, please let me know.