Messages in this thread | | | Date | Thu, 18 Nov 2004 10:39:44 -0600 | From | Jack Steiner <> | Subject | Re: Externalize SLIT table |
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(Resend of mail sent Nov 10, 2004 - as far as I can tell, it went nowhere)
On Wed, Nov 10, 2004 at 04:05:43PM +1100, Mark Goodwin wrote: > > On Tue, 9 Nov 2004, Matthew Dobson wrote: > >On Tue, 2004-11-09 at 12:34, Mark Goodwin wrote: > >>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? > >> > >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. > > How about we define cpu-distance to be "relative distance to the > lowest level cache on another CPU". On a system that has nodes with > multiple sockets (each supporting multiple cores or HT "CPUs" sharing > some level of cache), when the scheduler needs to migrate a task it would > first choose a CPU sharing the same cache, then a CPU on the same node, > then an off-node CPU (i.e. falling back to node distance).
I think I like your definition better than the one I originally proposed (cpu distance was distance between the local memories of the cpus).
But how do we determine the distance between the caches.
> > Of course, I have no idea if that's anything like an optimal or desirable > task migration policy. Probably depends on cache-trashiness of the task > being migrated. > > -- Mark
-- Thanks
Jack Steiner (steiner@sgi.com) 651-683-5302 Principal Engineer SGI - Silicon Graphics, Inc.
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