On Tuesday 11 July 2006 00:55, KAMEZAWA Hiroyuki wrote:
> On Mon, 10 Jul 2006 11:03:03 -0600
> Bjorn Helgaas <[email protected]> wrote:
>
> > On Sunday 09 July 2006 23:19, KAMEZAWA Hiroyuki wrote:
> > > Could you try this patch ? (against 2.6.18-rc1)
> >
> > Your patch does fix it. But I'm worried about removing
> > empty nodes at boot-time. I want to support the following
> > scenario:
> >
> > node 0: 1 enabled CPU, 3 disabled CPUs, no local memory
> > node 1: 4 disabled CPUs, no local memory
> > node 2: no CPUs, big interleaved memory across nodes 0 & 1
> >
> > At run-time, I'd like to be able to enable any or all of the
> > 7 disabled CPUs. If you remove the "empty" node 1 at boot-time,
> > it sounds like I won't be able to enable its CPUs later.
> >
>
> Hmm.. in my understanding, all structures for *possible* cpus are allocated
> at boot time. Then, only problem seems that a cpu is tied to
> not-exisiting-node at boot time.
> (see arch/ia64/kernel/numa.c, build_cpu_to_node_map())
>
> ====
> void __init build_cpu_to_node_map(void)
> {
> int cpu, i, node;
>
> for(node=0; node < MAX_NUMNODES; node++)
> cpus_clear(node_to_cpu_mask[node]);
>
> for(cpu = 0; cpu < NR_CPUS; ++cpu) {
> node = -1;
> for (i = 0; i < NR_CPUS; ++i)
> if (cpu_physical_id(cpu) == node_cpuid[i].phys_id) {
> node = node_cpuid[i].nid;
> break;
> }
> cpu_to_node_map[cpu] = (node >= 0) ? node : 0;
> if (node >= 0)
> cpu_set(cpu, node_to_cpu_mask[node]);
> }
> }
> =====
>
> Then what we have to do here are
> 1. remap cpu to the first existing node at hot-add event
> or
> 2. implement node-hot-add triggered by cpu-hot-add.
> Because we already have implemented node-hot-add triggered by memory-hotadd
> we can do it by small effort.
I haven't paid much attention to the memory/cpu/node hotplug stuff,
but (2) sounds reasonable.
> I think above will work for your environment.
> do you have any idea other than "don't remove empty node at boot time" ?
> or reserve empty node is the best way ?
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