Re: What to do with slow Chip/ST RAM

On Wed, 11 Mar 2009, Frank Wille wrote:

>>   Would anyone be interested in adding support to use chip/ST
>>   RAM on the amiga/atari in a similar fashion (obviously some of
>>   it is likely to be reserved for device DMA).
>
> I doubt that it would work very well for Amiga, because (I think) the amount
> of available Chip RAM is not constant. There may be allocations for floppy
> disk, audio or video DMA buffers at any time.
>
> The altmem device works with a fixed contiguous memory region?

 	It would probably be best to allocate most of the slow RAM to the
 	altmem device on boot and leave just enough to work as DMA space
 	for the devices. The important question is how *much* slower is
 	the slow ram. tsutsui@ commented that mvme86k already handles
 	split between fast and *very* slow (uncached!) ram by just
 	assigning priorities in uvm() so the fast ram is all used first.
 	Maybe that is a better approach for amiga and atari (maybe they
 	are already doing that?)

 	An interesting benchmark would be to run a system with the
 	memory bank priorities set appropriately, and then run it
 	again with the slow ram unsued apart from dma allocations
 	and see if having more ram (albeit slower) offsets the
 	speed penalty of accessing it.

 	In an ideal world the system could be tunable, so those with
 	large quantities for fast ram would not use slow at all, and
 	those with very little fast ram would...


-- 
 		David/absolute       -- www.NetBSD.org: No hype required --