Re: New NUMA scheduler and hotplug CPU

[Andrew Theurer <habanero@us.ibm.com>]

On Monday 26 January 2004 18:09, Martin J. Bligh wrote:
> > For example, you boot on just the boot cpu, which by default is in the
> > first node on the first runqueue.  All other cpus, whether being "booted"
> > for the for the first time or hotplugged (maybe now there's really no
> > difference), the hotplugging tells where the cpu should be, in what node
> > and what runqueue.  HT cpus work even better, because you can hotplug
> > siblings, once at a time if you wanted, to the same runqueue.  Or you
> > have cpus sharing a die, same thing, lots of choices here.  This removes
> > any per-arch updates to the kernel for things like scheduler topology,
> > and lets them go somewhere else more easily changes, like userspace.
>
> Ummm ... but *none* of that is dictated as policy stuff - it's all just
> the hardware layout of the machine. You cannot "decide" as the sysadmin
> which node a CPU is in, or which HT sibling it has. It's just there ;-)
> The only thing you could possibly dictate is the CPU number you want
> assigned to the new CPU, which frankly, I think is pointless - they're
> arbitrary tags, and always have been.

How many cpus share a runqueue IMO could be a policy thing.  Some HT cpus may 
be better sharing a runqueue where others (lots and lots of siblings in one 
core) may not.