Re: New NUMA scheduler and hotplug CPU

[Nick Piggin]

Andrew Theurer wrote:

> On Monday 26 January 2004 18:07, Nick Piggin wrote:
>
> > > > Well OK, this would require a per architecture function to handle
> > > > CPU hotplug. It could possibly just default to arch_init_sched_domains,
> > > > and just completely reinitialise everything which would be the simplest.
> > > Call me crazy, but why not let the topology be determined via userspace at
> > > a more appropriate time?  When you hotplug, you tell it where in the
> > > scheduler to plug it.  Have structures in the scheduler which represent
> > > the nodes-runqueues-cpus topology (in the past I tried a node/rq/cpu
> > > structs with simple pointers), but let the topology be built based on
> > > user's desires thru hotplug.
> > Well isn't userspace's idea of topology just what the kernel tells it?
> > I'm not sure what it would buy you... but I guess it wouldn't be too
> > much harder than doing it in kernel, just a matter of making the userspace
> > API.
>
> Sort of, the cpus to node is pretty much what the kernel says it is, but the 
> cpu to runqueue mapping IMO is not a clear cut thing.

But userspace still can't know more than the kernel tells it.
Apart from that, the SMT stuff in the sched domains patch means
SMT CPUs need not share runqueues.


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