Re: [PATCH RFC 4/5] powerpc:numa Add helper functions to maintain chipid to nid mapping

[Raghavendra K T]

On 09/28/2015 11:02 PM, Nishanth Aravamudan wrote:
> On 27.09.2015 [23:59:12 +0530], Raghavendra K T wrote:
> > Create arrays that maps serial nids and sparse chipids.
> >
> > Note: My original idea had only two arrays of chipid to nid map. Final
> > code is inspired by driver/acpi/numa.c that maps a proximity node with
> > a logical node by Takayoshi Kochi <t-kochi@xxxxxxxxxxxxx>, and thus
> > uses an additional chipid_map nodemask. The mask helps in first unused
> > nid easily by knowing first unset bit in the mask.
> >
> > No change in functionality.
> >
> > Signed-off-by: Raghavendra K T <raghavendra.kt@xxxxxxxxxxxxxxxxxx>
> > ---
> >   arch/powerpc/mm/numa.c | 48 +++++++++++++++++++++++++++++++++++++++++++++++-
> >   1 file changed, 47 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/powerpc/mm/numa.c b/arch/powerpc/mm/numa.c
> > index dd2073b..f015cad 100644
> > --- a/arch/powerpc/mm/numa.c
> > +++ b/arch/powerpc/mm/numa.c
> > @@ -63,6 +63,11 @@ static int form1_affinity;
> >   static int distance_ref_points_depth;
> >   static const __be32 *distance_ref_points;
> >   static int distance_lookup_table[MAX_NUMNODES][MAX_DISTANCE_REF_POINTS];
> > +static nodemask_t chipid_map = NODE_MASK_NONE;
> > +static int chipid_to_nid_map[MAX_NUMNODES]
> > +				= { [0 ... MAX_NUMNODES - 1] = NUMA_NO_NODE };
>
> Hrm, conceptually there are *more* chips than nodes, right? So what
> guarantees we won't see > MAX_NUMNODES chips?

You are correct that nid <= chipids.
and #nids = #chipids when all possible slots are populated. Considering
we assume that maximum chip slots are no more than MAX_NUMNODES,


how about having

#define MAX_CHIPNODES MAX_NUMNODES
and
chipid_to_nid_map[MAX_CHIPNODES] = { [0 ... MAX_CHIPNODES - 1] = ..

> > +static int nid_to_chipid_map[MAX_NUMNODES]
> > +				= { [0 ... MAX_NUMNODES - 1] = NUMA_NO_NODE };
> >
> >   /*
> >    * Allocate node_to_cpumask_map based on number of available nodes
> > @@ -133,6 +138,48 @@ static int __init fake_numa_create_new_node(unsigned long end_pfn,
> >   	return 0;
> >   }
> >
> > +int chipid_to_nid(int chipid)
> > +{
> > +	if (chipid < 0)
> > +		return NUMA_NO_NODE;
>
> Do you really want to support these cases? Or should they be
> bugs/warnings indicating that you got an unexpected input? Or at least
> WARN_ON_ONCE?

Right. Querying for nid of an invalid chipid should be atleast
WARN_ON_ONCE(). But 'll check once if there is any valid scenario
before the change.

> > +	return chipid_to_nid_map[chipid];
> > +}
> > +
> > +int nid_to_chipid(int nid)
> > +{
> > +	if (nid < 0)
> > +		return NUMA_NO_NODE;
> > +	return nid_to_chipid_map[nid];
> > +}
> > +
> > +static void __map_chipid_to_nid(int chipid, int nid)
> > +{
> > +	if (chipid_to_nid_map[chipid] == NUMA_NO_NODE
> > +	     || nid < chipid_to_nid_map[chipid])
> > +		chipid_to_nid_map[chipid] = nid;
> > +	if (nid_to_chipid_map[nid] == NUMA_NO_NODE
> > +	    || chipid < nid_to_chipid_map[nid])
> > +		nid_to_chipid_map[nid] = chipid;
> > +}
>
> chip <-> node mapping is a static (physical) concept, right? Should we
> emit some debugging if for some reason we get a runtime call to remap
> an already mapped chip to a new node?

Good point. Already mapped chipid to a different nid is unexpected
whereas mapping chipid to same nid is expected.(because mapping comes
from cpus belonging to same node).

WARN_ON() should suffice here?


> > +
> > +int map_chipid_to_nid(int chipid)
> > +{
> > +	int nid;
> > +
> > +	if (chipid < 0 || chipid >= MAX_NUMNODES)
> > +		return NUMA_NO_NODE;
> > +
> > +	nid = chipid_to_nid_map[chipid];
> > +	if (nid == NUMA_NO_NODE) {
> > +		if (nodes_weight(chipid_map) >= MAX_NUMNODES)
> > +			return NUMA_NO_NODE;
>
> If you create a KVM guest with a bogus topology, doesn't this just start
> losing NUMA information for very high-noded guests?

'll try to see if it is possible to hit this case, ideally we should
not allow more than MAX_NUMNODES for chipids and we should abort early.

> > +		nid = first_unset_node(chipid_map);
> > +		__map_chipid_to_nid(chipid, nid);
> > +		node_set(nid, chipid_map);
> > +	}
> > +	return nid;
> > +}
> > +
> >   int numa_cpu_lookup(int cpu)
> >   {
> >   	return numa_cpu_lookup_table[cpu];
> > @@ -264,7 +311,6 @@ out:
> >   	return chipid;
> >   }
> >
> > -
>
> stray change?

yep, will correct that.


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