Re: PAT support

[Masao Uebayashi <uebayasi%tombi.co.jp@localhost>]

On Wed, May 19, 2010 at 01:23:19PM +1000, matthew green wrote:
> what's PAT?  could you add a comment to pat.c, explaining what this
> code is for?

From http://en.wikipedia.org/wiki/Page_Attribute_Table:

        The Page Attribute Table (PAT, also known as Page Allocation
        Table[citation needed]) is a processor supplementary capability
        extension to the page table format of certain x86 and x86-64
        microprocessors. Like memory type range registers (MTRRs), they
        allow for fine-grained control over how areas of memory are
        cached, and are a companion feature to the MTRRs.[1]

        Unlike MTRRs, which provide the ability to manipulate the behavior
        of caching for a limited number of fixed physical address ranges,
        Page Attribute Tables allow for such behavior to be specified
        on a per-page basis, greatly increasing the ability of the
        operating system to select the most efficient behavior for any
        given task.

My understanding is, this is most typically for GPUs.  Time to revisit
the hacks in our drm(4) code...

Masao

-- 
Masao Uebayashi / Tombi Inc. / Tel: +81-90-9141-4635