linux-kernel - Re: [PATCH] x86: mtrr cleanup for converting continuous to discrete

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Date:	Thu, 1 May 2008 14:44:23 -0700
From:	"Yinghai Lu" <yhlu.kernel@...il.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Ingo Molnar" <mingo@...e.hu>,
	"Thomas Gleixner" <tglx@...utronix.de>,
	"Gabriel C" <nix.or.die@...glemail.com>,
	"Mika Fischer" <mika.fischer@...pnet.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86: mtrr cleanup for converting continuous to discrete - auto detect v2

On Thu, May 1, 2008 at 2:33 PM, H. Peter Anvin <hpa@...or.com> wrote:
> Yinghai Lu wrote:
>
> >
> > >  Overall, I'm feeling there is something really completely wrong if this
> > > needs manual tunables of any sort.
> > >
> >
> > the problem is BIOS set MTRR like BIG WB - SOME SAMLL UC to spare mtrr
> regs.
> >
> > but later X server driver want to set some range to WC. that already
> > is fallen in UC...
> >
>
>  That's not the point.  I understand you want to flatten the layout.  The
> point is: why do you need manual tunables for the algorithm to do the right
> thing?

optimal result is not losing covering for ranges that is originally
covered, and still keep as many of spare mtrr entries for X server
driver.
we only have 8 mtrrs, could lose some covering because of run out of mtrr regs.
So we need to search it according to chunk/gran with ram ranges that
is defined by old mtrr layout.

and if we can not find the optimal setting, user could select one
setting (chunk/gran size) to boot next time, but he will lose some
covering.
for some regions. later trim_mtrr will remove those range from e820 map

YH
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