Re: MTRR fixup?

On Wednesday 03 September 2008 10:02:15 pm Bernd Walter wrote:
> On Thu, Sep 04, 2008 at 03:55:07AM +0200, Bernd Walter wrote:
> > On Thu, Sep 04, 2008 at 01:46:42AM +0200, Bernd Walter wrote:
> > > On Wed, Sep 03, 2008 at 09:47:59PM +0100, David Malone wrote:
> > > > On Wed, Sep 03, 2008 at 05:49:44AM +0200, Bernd Walter wrote:
> > > > > Some boards (including my Intel DG33BU) seem to have problems
> > > > > setting up the mtrr to cache all RAM.
> > > > > My system runs fast with 2G and ist about 6 times slower in
> > > > > buildworld with 6G RAM.
> > > > > I will try a BIOS update once Intels tells me why their update ISO
> > > > > just turn the system off instead of updating the BIOS - sigh.
> > > > > But it seems that Linux is doing some kind of fixup for MTRR:
> > > > > http://lkml.org/lkml/2008/1/18/170
> > > > > Can we do something similar?
> > > >
> > > > You may be able to fix this by just using the memcontrol command -
> > > > it already lets you program the MTRRs.
> > >
> > > Oh damn - a new fancy tool to play with ;-)
> > >
> > > Interesting - the values look good:
> > > [...]
> > > 0x0/0x80000000 ticso write-back active
> > > 0x80000000/0x40000000 ticso write-back active
> > > 0xc0000000/0x10000000 ticso write-back active
> > > 0xcf800000/0x800000 BIOS uncacheable set-by-firmware active
> > > 0xcf400000/0x400000 BIOS uncacheable set-by-firmware active
> > > 0x100000000/0x80000000 ticso write-back active
> > > 0x180000000/0x20000000 ticso write-back active
> > > 0x0/0x1000000000 - uncacheable
> >
> > Ok - there it is - something is missing:
> >   ram0
> >       I/O memory addresses:
> >           0x0-0x9c3ff
> >           0x100000-0xcf212fff
> >           0xcf215000-0xcf2fafff
> >           0xcf3e5000-0xcf3e8fff
> >           0xcf3f2000-0xcf3f2fff
> >           0xcf3ff000-0xcf3fffff
> >           0x100000000-0x1abffffff
> >
> > ram goes up to 0x1abffffff mtrr just goes up to 0x1a0000000 - 1, so the
> > last 192MB are uncached.
> > But memcontrol complains when trying to add the range:
> > [55]cicely14# memcontrol set -b 0x1a0000000 -l 0xc000000 -o ticso
> > write-back memcontrol: can't set range: Invalid argument
>
> Ok - I more or less got it.
> I have to set 2^n ranges.
> The first one goes:
> [56]cicely14# memcontrol set -b 0x1a0000000 -l 0x8000000 -o ticso
> write-back The second not:
> [57]cicely14# memcontrol set -b 0x1a8000000 -l 0x4000000 -o ticso
> write-back memcontrol: can't set range: No space left on device
> Exit 1

You ran out of variable range MTRRs.  You probably don't have any devices 
using memory space above the end of RAM, so you can probably do:

memcontrol set -b 0x1a0000000 -l 0x10000000

and just lie about that last 64MB or so of address space.

-- 
John Baldwin