On Fri, Apr 27, 2007 at 10:25:44PM +1000, Nick Piggin wrote:
Linus's favourite jokes about powerpc mmu being crippled forever, aside ;)
Different mmu. The desktop 32bit mmu Linus refered to has almost nothing
in common with the mmu on 64bit systems.
Right this could help but it is not addressing the basic requirement for
devices that need large contiguuos chunks of memory for I/O.
Did you read the last paragraph? Or anything Andrew's been writing?
"After that, I'd find it amusing if HBAs worth thousands of $ have
trouble looking up sglists at the relatively glacial pace that IO
requires, and/or can't spare a few more K for reasonable sglist
sizes, but if that is really the case, then we could use iommus
and/or just attempt to put physically contiguous pages in pagecache,
rather than require it."
Real highend HBAs don't have that problem. But for example aacraid
which is very common on mid-end servers is a _lot_ faster when it
gets continous memory. Some benchmark was 10 or more percent faster
on windows due to this.