Hm. "Obsessed" is an unkind word. I just haven't seen many other cards
where MTRRs would be an advantage. For example, I don't see a use for
MTRRs with frame grabbers because you read from these cards. Making
frame-grabber memory cachable is probably unwise. It seems to me that
most cards with mappable memory provide it for reading.
Cards which come to mind that have writable memory are:
- framebuffers
- network cards
- ???
Would write-combining help for NICs? When I timed the data-transfer
function for a network driver (admittedly a cheap PCI NE2000), it took
a millisecond to transfer a full packet. That's roughly a megabyte per
second. Write-combining won't help for such a shite interface. Is that
the exception or the rule?
And then there is the main RAM case. Here the BIOS is supposed to set
up the MTRRs. Is it wise to (automatically) fiddle with that? If I
disable caching in the BIOS, I don't want the kernel enabling
automatically either.
Anyway, if you don't want me to "obsess", then why not list the cards
where MTRRs would be useful and why? It would help if I had a picture
of the things you have in mind.
> > cheapo Centaurs have 8. Time for AMD to pull their finger out...
>
> AMD are quite obviously aiming at a standard desktop PC mentality,
> one MTRR for the video ram, one for the texture ram, and a seperate
> MSRR for the RAM area.
What would they do then for a linear FB with the last page filled with
control registers? Looks like you often need two MTRRs for the basic
card before you even start thinking about texture RAM.
Regards,
Richard....
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