Re: New NUMA scheduler and hotplug CPU

[Nick Piggin <piggin@cyberone.com.au>]

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.