/proc/mtrr

[Martin Mačok]

On Mon, Jul 09, 2001 at 12:49:55AM +0200, Jan Krupka wrote:
> mel bych dotaz co to vlastne je mtrr? 

Soubor mtrr.txt v Documentation/ u zdrojaku jadra.

  On Intel P6 family processors (Pentium Pro, Pentium II and later)
  the Memory Type Range Registers (MTRRs) may be used to control
  processor access to memory ranges. This is most useful when you have
  a video (VGA) card on a PCI or AGP bus. Enabling write-combining
  allows bus write transfers to be combined into a larger transfer
  before bursting over the PCI/AGP bus. This can increase performance
  of image write operations 2.5 times or more.

  ... (pokracovani v mtrr.txt)

> Zda se mi, ze tam mam nejake divne hodnoty. Je tohle v poradku nebo je tam 
> neco shnileho?
> 
> cat /proc/mtrr
> reg00: base=0x00000000 (   0MB), size=16711808MB: write-back, count=1
> reg05: base=0xd0000000 (3328MB), size=16711744MB: write-combining, count=1

Ta polozka "size" vypada opravdu divne - co mate za kernel a co mate
za hardware?

U mne:

Red Hat 7.1 Linux, kernel 2.4.3-12, Matrox G450 DL, Athlon 850:
% cat /proc/mtrr                               
reg00: base=0x00000000 (   0MB), size= 256MB: write-back, count=1
reg01: base=0xe4000000 (3648MB), size=  16MB: write-combining, count=2
reg07: base=0xe6000000 (3680MB), size=  32MB: write-combining, count=2

Z tech cisel teda taky nejsem chytry, ve zminovanem souboru ukazuji
takoveto priklady:
% cat /proc/mtrr
reg00: base=0x00000000 (   0MB), size= 128MB: write-back, count=1
reg01: base=0x08000000 ( 128MB), size=  64MB: write-back, count=1
reg02: base=0xf8000000 (3968MB), size=   4MB: write-combining, count=1

%  cat /proc/mtrr
reg00: base=0x00000000 (   0MB), size=  64MB: write-back, count=1
reg01: base=0xfb000000 (4016MB), size=  16MB: write-combining, count=1
reg02: base=0xfb000000 (4016MB), size=   4kB: uncachable, count=1


-- 
   Martin Mačok
  underground.cz
    openbsd.cz