Re: CPA patchset

Ingo Molnar
2008-01-10T10:57:59Z

* Andi Kleen <ak@suse.de> wrote:

> > > > WBINVD isnt particular fast (takes a few msecs), but why is
> > > > that a problem? Drivers dont do high-frequency ioremap-ing.
> > > > It's typically only done at driver/device startup and that's
> > > > it.
> > >
> > > Actually graphics drivers can do higher frequency allocation of WC
> > > memory (with PAT) support.
> >
> > but that's not too smart: why dont they use WB plus cflush instead?
>
> Because they need to access it WC for performance.

I think you have it fundamentally backwards: the best for performance is
WB + cflush. What would WC offer for performance that cflush cannot do?

also, it's irrelevant to change_page_attr() call frequency. Just map in
everything from the card and use it. In graphics, if you remap anything
on the fly and it's not a slowpath you've lost the performance game even
before you began it.

Ingo