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SubjectRe: [PATCH 010 of 11] knfsd: make rpc threads pools numa aware
On Sunday July 30, akpm@osdl.org wrote:
> On Mon, 31 Jul 2006 10:42:34 +1000
> NeilBrown <neilb@suse.de> wrote:
>
> > +static int
> > +svc_pool_map_init_percpu(struct svc_pool_map *m)
> > +{
> > + unsigned int maxpools = num_possible_cpus();
> > + unsigned int pidx = 0;
> > + unsigned int cpu;
> > + int err;
> > +
> > + err = svc_pool_map_alloc_arrays(m, maxpools);
> > + if (err)
> > + return err;
> > +
> > + for_each_online_cpu(cpu) {
> > + BUG_ON(pidx > maxpools);
> > + m->to_pool[cpu] = pidx;
> > + m->pool_to[pidx] = cpu;
> > + pidx++;
> > + }
>
> That isn't right - it assumes that cpu_possible_map is not sparse. If it
> is sparse, we allocate undersized pools and then overindex them.

I don't think so.

At this point we are largely counting the number of online cpus
(in pidx (pool index) - this is returned). The two-way mapping
to_pool and pool_to provides a mapping between the possible-sparse cpu
list and a dense list of pool indexes.

If further cpus come on line they will be automatically included in
pool-0. (as to_pool[n] will still be zero).

Does that make it at all clearer?

Thanks,
NeilBrown
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