Re: [PATCH] powerpc/numa: Fix percpu allocations to be NUMA aware

Nicholas Piggin [off-list ref] writes:

On Fri, 02 Jun 2017 19:54:32 +1000
Michael Ellerman [off-list ref] wrote:

quoted

quoted

quoted

@@ -672,10 +672,19 @@ static void __init pcpu_fc_free(void *ptr, size_t size)
 
 static int pcpu_cpu_distance(unsigned int from, unsigned int to)
 {
-	if (cpu_to_node(from) == cpu_to_node(to))
-		return LOCAL_DISTANCE;
-	else
-		return REMOTE_DISTANCE;
+#ifndef CONFIG_NUMA
+	return LOCAL_DISTANCE;
+#else
+	int from_nid, to_nid;
+
+	from_nid = early_cpu_to_node(from);
+	to_nid   = early_cpu_to_node(to);
+
+	if (from_nid == -1 || to_nid == -1)
+		return LOCAL_DISTANCE;	/* Or assume remote? */
+
+	return node_distance(from_nid, to_nid);  

If you made node_distance() return LOCAL_NODE for !NUMA, this
should fall out and not require the ifdef?  

Maybe yeah. This is designed to be minimal for backporting though.

Okay fair enough. Is it expected to get back -1 from this ever? I think
all we need is local vs not local to direct whether to pack CPUs into
the same chunks or not so I wonder if the equality test is simpler.

Yeah you're right, I'll do a v2.

I think I was worried about the fact that our node_distance() does
complicated stuff for multi-level NUMA, but that doesn't actually matter
for the per-cpu calculation as you say so it's probably better to keep
it simple.

cheers