[coreboot] Timings v2

Kevin O'Connor kevin at koconnor.net
Tue Apr 21 03:44:48 CEST 2009

On Mon, Apr 20, 2009 at 10:17:43AM -0600, Marc Jones wrote:
> On Sun, Apr 19, 2009 at 8:38 AM, Kevin O'Connor <kevin at koconnor.net> wrote:
> > Another optimization I could make would be to reduce the 90ms it takes
> > to copy the vga rom from flash.  Using 4 byte reads instead of 1 byte
> > reads will likely help.  However, enabling an mtrr for the flash would
> > likely lead to the best results.
> We have been discussing this in another thread. The 4byte read will
> make the most improvement and the cache only helps a lot if the ROM is
> compressed. You are still bound by the width and speed of the ROM
> access. LPC/FWH is typically setup to be very slow.

I implemented a 4byte copy on Sunday night - it dropped the copy time
from 90ms to 50ms.  It's in the latest SeaBIOS git.

I was hoping that caching flash would allow the procesor to do
cache-line sized reads.  But, you have a good point about the LPC/FWH
being a limit.  Does anyone know if 50ms is the lower limit on reading
63488 bytes from flash?  It still seems high.


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