Re: 36 bit MTRRs, Re: test10-pre1 problems on 4-way SuperServer8050

From: Tigran Aivazian (
Date: Wed Oct 11 2000 - 11:42:53 EST

On Wed, 11 Oct 2000, Boszormenyi Zoltan wrote:

> On Wed, 11 Oct 2000, Tigran Aivazian wrote:
> > I will continue to narrow down by removing some things (like mtrr) from
> > the equation. Rik, the problem is that when one enables PAE (or just
> > highmem-4G) support on a 4-way 6G RAM machine becomes 38-40 times slower.
> Will you please try this patch? This is almost the same as I
> sent to you before, it is just against 2.4.0-test10-pre1 and
> it lacks the corrections to e.g. the frame buffer drivers.

Hi Zoltan,

I have tried your patch and although it works:

# cat /proc/mtrr
reg00: base=0x00000000 ( 0MB), size=4096MB: write-back, count=1
reg01: base=0x00100000000 ( 4096MB), size= 2048MB: write-back,
reg02: base=0xfc000000 (4032MB), size= 64MB: uncachable, count=1

unfortunately, it doesn't solve the problem. The machine is still
unbearably slow (up to 40x slower!) and one of the eepro100 interfaces is
still not working.

Another interesting idea was suggested by Mark Hemment - to switch

memlist_add_head() -> memlist_add_tail()

in expand()/__free_pages_ok() (see mm/page_alloc.c) and it did make a
difference -- both eepro100 started to work fine but the machine remained
just as slow as before.

So, the problem is complex but I am told that Rik and others are aware
that at present there is no working support for highmem. Strangely, my
desktop dual PIII550 with 1G RAM works just fine with highmem... nice and
fast, no problems whatsoever and it is filled up with all kinds of
devices, from soundcard to bttv848, 3dfx, eepro100, ne2k, 8139 etc
etc. Everything just works.


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