linux-kernel - Re: CPA patchset

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Date:	Thu, 10 Jan 2008 10:55:01 +0100
From:	Andi Kleen <ak@...e.de>
To:	Dave Airlie <airlied@...il.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Andi Kleen <ak@...e.de>,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Venki Pallipadi <venkatesh.pallipadi@...el.com>,
	suresh.b.siddha@...el.com, Arjan van de Ven <arjan@...radead.org>,
	Dave Jones <davej@...hat.com>
Subject: Re: CPA patchset

On Thu, Jan 10, 2008 at 07:44:03PM +1000, Dave Airlie wrote:
> >
> > finally managed to get the time to review your CPA patchset, and i
> > fundamentally agree with most of the detail changes done in it. But here
> > are a few structural high-level observations:
> >
> > - firstly, there's no rationale given. So we'll change ioremap()/etc.
> >   from doing a cflush-range instruction instead of a WBINVD. But why?
> >   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. Whether module load
> >   time takes 1254 msecs instead of 1250 msecs is no big deal.
> 
> read graphics drivers, even though I think we may avoid the whole path

You mean avoid change_page_attr() ? 

> if we can and end up doing some of this in the drivers
> when they know more about the situation so can avoid safeties..

Please explain, but it sounds very dubious.

> but I still see this being used in AGP a fair bit at some point on
> some drivers..

Well GARTs and those are widely used even without AGP busses.

-Andi
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