Re: [Xen-devel] [PATCH v8] Some automatic NUMA placement documentation

[Dario Faggioli <dario.faggioli@xxxxxxxxxx>]

On Thu, 2012-07-26 at 17:00 +0100, Ian Jackson wrote: 
> Dario Faggioli writes ("[PATCH v8] Some automatic NUMA placement 
> documentation"):
> > About rationale, usage and (some small bits of) API.
> 
> > +Also, if `numa_placement` is set to `true`, the domain must not
> > +have any cpu affinity (i.e., `domain_build_info->cpumap` must
> > +have all its bits set, as it is by default), or domain creation
> > +will fail returning `ERROR_INVAL`.
> 
> This is no longer true, is it ?
> 
I think it is. Actually, it was you that suggested turning the code into
that... :-P

It's this thing I'm trying to document:

    if (libxl_defbool_val(info->numa_placement)) {
        int rc;

        if (!libxl_bitmap_is_full(&info->cpumap)) {
            LOG(ERROR, "Can run NUMA placement only if no vcpu "
                       "affinity is specified");
            return ERROR_INVAL;
        }

        rc = numa_place_domain(gc, domid, info);
        if (rc)
            return rc;
    }

Am I missing something?

> > +Analyzing various possible placement solutions is what makes the
> > +algorithm flexible and quite effective. However, that also means
> > +it won't scale well to systems with arbitrary number of nodes.
> > +For this reason, if machines with more than 16 NUMA nodes will
> > +ever exist, placement will automatically disables itself when
> > +running libxl on them.
> 
> This last is very awkwardly phrased.  How about:
> 
>    For this reason, automatic numa placement is disabled (with
>    a warning) if it is requested on a host with more than 16 NUMA
>    nodes.
> 
Fine with it. Will change it.

Dario

-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://retis.sssup.it/people/faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)

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