[CentOS] [OT] Memory Models and Multi/Virtual-Cores -- WAS: 4.0-> 4.1 update failing

Bryan J. Smith b.j.smith at ieee.org
Wed Jun 29 04:48:30 UTC 2005


On Wed, 2005-06-29 at 12:20 +0800, Feizhou wrote:
> I thought they have done away with the high memory bounce buffers?

Correct.  On x86-64, they have.

> Can you explain what Andi means by this?
> ----quote----
> Current X86-64 implementations only support 40 bit of address space,
> but we support upto 46bits. This expands into MBZ space in the page tables.
> -Andi Kleen, Jul 2004
> ----quote----
> Does it mean that we don't need no fancy tweaks to get direct addressing 
> for over 1G or over 4G?

Correct.  I haven't looked at how Linux/x86-64's paging works, but as
long as they at least support 40-bit, they're good for the current
generation of AMD64.

Some EM64T processors only do 36-bit, the new ones do 40-bit (with a new
TLB-page table).

> Is that hack for Athlons limited/useful only to Athlon MP boards with 
> the Linux option in BIOS or do Opterons also need that?

It hack is _solely_ for Athlon MP, and it's quite limited in scope.
In a nutshell, it really enables features of the Athlon MP that
_breaks_everything_.  Hence why it's rare, and Linux is the only OS with
the hack.

Opteron with its x86-64 PAE (52-bit) mode is completely linear, up to
40-bit in its current, legacy EV6 logic implementation.  The 52-bit
virtual addressing using PAE allows 32-bit, legacy 36-bit PAE as well as
new 52-bit PAE applications to run.


-- 
Bryan J. Smith                                     b.j.smith at ieee.org 
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