Re: [00/17] Large Blocksize Support V3

Christoph Hellwig
2007-04-27T13:40:40Z

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.