linux-kernel - Re: [RFC PATCH 1/2] NUMA balancing: fix NUMA topology type for memory tiering system

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Date:   Fri, 28 Jan 2022 16:06:30 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Huang Ying <ying.huang@...el.com>
Cc:     Mel Gorman <mgorman@...e.de>, linux-kernel@...r.kernel.org,
        Ingo Molnar <mingo@...hat.com>,
        Rik van Riel <riel@...riel.com>,
        Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Subject: Re: [RFC PATCH 1/2] NUMA balancing: fix NUMA topology type for
 memory tiering system

On Fri, Jan 28, 2022 at 10:38:41AM +0800, Huang Ying wrote:
>  kernel/sched/topology.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
> index 9f26e6b651fe..ba975a29d444 100644
> --- a/kernel/sched/topology.c
> +++ b/kernel/sched/topology.c
> @@ -1738,7 +1738,13 @@ void init_numa_topology_type(void)
>  	}
>  
>  	for_each_online_node(a) {
> +		if (!node_state(a, N_CPU))
> +			continue;
> +
>  		for_each_online_node(b) {
> +			if (!node_state(b, N_CPU))
> +				continue;
> +
>  			/* Find two nodes furthest removed from each other. */
>  			if (node_distance(a, b) < n)
>  				continue;

I think you forgot some.. by not skipping CPU-less nodes in
sched_init_numa() the whole premise of init_numa_topology_type() goes
out the window as well, by virtue of getting sched_domains_numa_levels
and sched_max_numa_distance wrong.

Did I get them all?

Do we want something like:

#define for_each_possible_cpu_node(n)	for (n = 0; n < nr_node_ids; n++) if (!node_state(n, N_CPU)) continue; else
#define for_each_online_cpu_node(n)	for_each_online_node(n) if (!node_state(n, N_CPU)) continue; else

To clean that up?

---
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -1684,8 +1684,12 @@ static void sched_numa_warn(const char *
 
 	for (i = 0; i < nr_node_ids; i++) {
 		printk(KERN_WARNING "  ");
-		for (j = 0; j < nr_node_ids; j++)
-			printk(KERN_CONT "%02d ", node_distance(i,j));
+		for (j = 0; j < nr_node_ids; j++) {
+			if (!node_state(i, N_CPU) || !node_state(j, N_CPU))
+				printk(KERN_CONT "(%02d) ", node_distance(i,j));
+			else
+				printk(KERN_CONT " %02d  ", node_distance(i,j));
+		}
 		printk(KERN_CONT "\n");
 	}
 	printk(KERN_WARNING "\n");
@@ -1737,7 +1741,13 @@ static void init_numa_topology_type(void
 	}
 
 	for_each_online_node(a) {
+		if (!node_state(a, N_CPU))
+			continue;
+
 		for_each_online_node(b) {
+			if (!node_state(b, N_CPU))
+				continue;
+
 			/* Find two nodes furthest removed from each other. */
 			if (node_distance(a, b) < n)
 				continue;
@@ -1756,6 +1766,9 @@ static void init_numa_topology_type(void
 			return;
 		}
 	}
+
+	pr_err("Failed to find a NUMA topology type, defaulting to DIRECT\n");
+	sched_numa_topology_type = NUMA_DIRECT;
 }
 
 
@@ -1778,9 +1791,15 @@ void sched_init_numa(void)
 
 	bitmap_zero(distance_map, NR_DISTANCE_VALUES);
 	for (i = 0; i < nr_node_ids; i++) {
+		if (!node_state(i, N_CPU))
+			continue;
+
 		for (j = 0; j < nr_node_ids; j++) {
 			int distance = node_distance(i, j);
 
+			if (!node_state(j, N_CPU))
+				continue;
+
 			if (distance < LOCAL_DISTANCE || distance >= NR_DISTANCE_VALUES) {
 				sched_numa_warn("Invalid distance value range");
 				return;
@@ -1863,6 +1882,12 @@ void sched_init_numa(void)
 				if (sched_debug() && (node_distance(j, k) != node_distance(k, j)))
 					sched_numa_warn("Node-distance not symmetric");
 
+				if (!node_state(j, N_CPU))
+					continue;
+
+				if (!node_state(j, N_CPU))
+					continue;
+
 				if (node_distance(j, k) > sched_domains_numa_distance[i])
 					continue;
 
@@ -1943,6 +1968,9 @@ static void __sched_domains_numa_masks_s
 			if (!node_online(j) || node == j)
 				continue;
 
+			if (!node_state(j, N_CPU))
+				continue;
+
 			if (node_distance(j, node) > sched_domains_numa_distance[i])
 				continue;
 
@@ -1974,6 +2002,9 @@ void sched_domains_numa_masks_set(unsign
 			if (!node_online(j))
 				continue;
 
+			if (!node_state(j, N_CPU))
+				continue;
+
 			/* Set ourselves in the remote node's masks */
 			if (node_distance(j, node) <= sched_domains_numa_distance[i])
 				cpumask_set_cpu(cpu, sched_domains_numa_masks[i][j]);