On Mon, Jul 26, 2004 at 01:23:41PM +0200, Maciej W. Rozycki wrote:
> > There is a general perception among Linux users that 64-bit is new an
> > not really needed which in part I blame on the bs Intel is spreading to
> > hide the fact that for a long time they simply had no 64-bit roadmap at
> > all.
>
> Huh? How's Intel's policy related to 64-bit Linux? Especially for other
> processors, like MIPS.
Their wrong claims that only server machines need 64-bit.
> Linux has supported 64-bit operation since ~1995 and around 1998 when I
> had an opportunity to use it on DEC Alpha, it (2.0.x) was already stable
> enough for regular use. That is the generic core and the Alpha bits, of
> course -- the maturity of other processor support may vary, but for MIPS
> it's not worse than the 32-bit support.
At least after I fixed kernel mode page tables last week. The 4MB limit
we had before that was just ridiculous.
> > There are still improvments to be made for BCM1250 support. Somebody
> > thought scattering the first 1GB of memory through the lowest 4GB of
> > physical address space like a three year old his toys over the floor
> > was a good thing ... The resulting holes in the memory map are wasting
> > significant amounts of memory for unused memory; the worst case number
> > that is reached for 64-bit kernel on a system with > 1GB of RAM is 96MB!
>
> Well, there are some resons given in the manual. Anyway, memory seems to
> be remappable to 0x100000000 in the DRAM controller. Still we probably
> have to keep low 256MB mapped and registered within Linux at 0 for bounce
> buffers for broken PCI hardware ("hidden" mapping for exception handlers
> and kernel segments would be easier).
>
> With only 256MB installed in my system it would be tough for me to code
> anything interesting, though. Perhaps another time.
I have 1GB and that's where 32-bit kernels are beginning to look really
like a bad idea on MIPS. Fortunately on the BCM1250 and all the other
64-bit processors there is an easy way out. Better even, some of the
embedded application performance numbers suggest significant performance
gains for 64-bit processing contrary to conventional wisdom about 64-bit
computing.
Ralf
