Re: Externalize SLIT table

From: Matthew Dobson
Date: Tue Nov 09 2004 - 19:06:07 EST

On Tue, 2004-11-09 at 12:34, Mark Goodwin wrote:
> On Tue, 9 Nov 2004, Matthew Dobson wrote:
> > ...
> > I don't think we should export the *exact same* node distance information
> > through the CPUs, though.
> We should still export cpu distances though because the distance between
> cpus on the same node may not be equal. e.g. consider a node with multiple
> cpu sockets, each socket with a hyperthreaded (or dual core) cpu.

Well, I'm not sure that just because a CPU has two hyperthread units in
the same core that those HT units have a different distance or latency
to memory...? The fact that it is a HT unit and not a physical core has
implications to the scheduler, but I thought that the 2 siblings looked
identical to userspace, no? If 2 CPUs in the same node are on the same
bus, then in all likelihood they have the same "distance".

> Once again however, it depends on the definition of distance. For nodes,
> we've established it's the ACPI SLIT (relative distance to memory). For
> cpus, should it be distance to memory? Distance to cache? Registers? Or
> what?
> -- Mark

That's the real issue. We need to agree upon a meaningful definition of
CPU-to-CPU "distance". As Jesse mentioned in a follow-up, we can all
agree on what Node-to-Node "distance" means, but there doesn't appear to
be much consensus on what CPU "distance" means.


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