Re: [PATCH] Support for GEODE CPUs

From: Lennart Sorensen
Date: Thu Mar 10 2005 - 00:27:42 EST

On Wed, Mar 09, 2005 at 09:59:26PM +0000, Alan Cox wrote:
> If you build 486 it will still use the TSC because it is available (The
> PIT is buggy but the kernel knows about that anyway and handles it).

Hmm, I thought that was the whole point of the different cpu type
choices in the kernel. Then again the MTRR is still available with a
386 kernel on a newer cpu as far as I remember, so I guess I will try a
486 optimized kernel next.

> There are a few Geode tricks to know for performance
> - Turn off the video

That is the plan long term, although the BIOS's serial console doesn't
seem to work well with grub at least on minicom. I think switching to
lilo may help that.

> - If you can't turn it off use solid areas of colour to speed the system
> up (The hardware uses RLE encoding to reduce ram fetch bandwidth)
> - Remember the cache is only 16K (12K when running X11 as 4K is borrowed
> for the blitter)

Even more reason to keep the video off (I think it steals some system
ram when on as well).

> - The onboard audio is a software SB emulation on older GX. It burns
> CPU.

I have audio disabled since I have no need for it.

> Also avoid touching various legacy registers as much as possible, many
> cause BIOS traps in SMM emulation code. The list I have is NDA but you
> can use rdtsc/inb or outb/rdtsc to work out which 8)

Only PCI and LPC devices in use, so I don't think I will be poking any
legacy registers directly, although I have no idea if the kernel would
be poking any of them as part of running the drivers. Hopefully not.

Thanks for the information.

Len Sorensen
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