Re: [Linux-ia64] BitKeeper tree for 2.4.x

Steffen Persvold
2002-10-17T18:16:48Z

On Mon, 14 Oct 2002, Bjorn Helgaas wrote:

> On Monday 14 October 2002 12:17 pm, Steffen Persvold wrote:
> > Well, without MAP_WRITECOMBINED, streaming PIO accesses to the PCI bus
> > drops from 330MByte/sec to approx. 100MByte/s using the Dolphin SCI card.
> >
> > This is an rather significant drop which makes the IA64 platform kind of
> > uninteresting for high performance clustering (the Dolphin SCI cards are
> > used for shared memory message passing between nodes).
> >
> > We can of course hack this in for our usage (in our kernel driver) if you
> > are totally against having it in the kernel headers, but I think since the
> > hardware allows different mapping types, the kernel should take advantage
> > of it.
>
> I'm really not opposed to having it in the kernel headers. The thing
> is, we were allowing WC mappings regardless of whether the hardware
> actually supported them. What we need is some mechanism for
> looking at the EFI memory map, which tells us what attributes are
> supported.

Which IA64 hardware doesn't support _PAGE_MA_WC in the PTE ? My IA64 docs
doesn't mention anything about that.

>
> We've got a mechanism for looking up the supported attributes
> (efi_mem_attributes()); what I'd really like is for somebody to
> hook that up with the mmap infrastructure so that we only allow
> the supported attributes.

Actually I think _PAGE_MA_WC is only applicable to IO memory the same way
as _PAGE_MA_UC is. Can't it be handled in the same way ? (you've already
done the fix for UC, right ?)

Regards,
--
Steffen Persvold | Scali AS
mailto:sp@scali.com | http://www.scali.com
Tel: (+47) 2262 8950 | Olaf Helsets vei 6
Fax: (+47) 2262 8951 | N0621 Oslo, NORWAY