linux-kernel - [RFC PATCH 2/2] Revert "sched/topology: Warn when NUMA diameter

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Message-Id: <20210203155432.10293-3-valentin.schneider@arm.com>
Date:   Wed,  3 Feb 2021 15:54:31 +0000
From:   Valentin Schneider <valentin.schneider@....com>
To:     linux-kernel@...r.kernel.org
Cc:     vincent.guittot@...aro.org, mgorman@...e.de, mingo@...nel.org,
        peterz@...radead.org, dietmar.eggemann@....com,
        morten.rasmussen@....com, linuxarm@...neuler.org,
        xuwei5@...wei.com, liguozhu@...ilicon.com, tiantao6@...ilicon.com,
        wanghuiqiang@...wei.com, prime.zeng@...ilicon.com,
        jonathan.cameron@...wei.com, guodong.xu@...aro.org,
        Barry Song <song.bao.hua@...ilicon.com>,
        Meelis Roos <mroos@...ux.ee>
Subject: [RFC PATCH 2/2] Revert "sched/topology: Warn when NUMA diameter > 2"

The scheduler topology code can now figure out what to do with such
topologies.

This reverts commit b5b217346de85ed1b03fdecd5c5076b34fbb2f0b.

Signed-off-by: Valentin Schneider <valentin.schneider@....com>
---
 kernel/sched/topology.c | 33 ---------------------------------
 1 file changed, 33 deletions(-)

diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index a8f69f234258..0fa41aab74e0 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -688,7 +688,6 @@ cpu_attach_domain(struct sched_domain *sd, struct root_domain *rd, int cpu)
 {
 	struct rq *rq = cpu_rq(cpu);
 	struct sched_domain *tmp;
-	int numa_distance = 0;
 
 	/* Remove the sched domains which do not contribute to scheduling. */
 	for (tmp = sd; tmp; ) {
@@ -720,38 +719,6 @@ cpu_attach_domain(struct sched_domain *sd, struct root_domain *rd, int cpu)
 			sd->child = NULL;
 	}
 
-	for (tmp = sd; tmp; tmp = tmp->parent)
-		numa_distance += !!(tmp->flags & SD_NUMA);
-
-	/*
-	 * FIXME: Diameter >=3 is misrepresented.
-	 *
-	 * Smallest diameter=3 topology is:
-	 *
-	 *   node   0   1   2   3
-	 *     0:  10  20  30  40
-	 *     1:  20  10  20  30
-	 *     2:  30  20  10  20
-	 *     3:  40  30  20  10
-	 *
-	 *   0 --- 1 --- 2 --- 3
-	 *
-	 * NUMA-3	0-3		N/A		N/A		0-3
-	 *  groups:	{0-2},{1-3}					{1-3},{0-2}
-	 *
-	 * NUMA-2	0-2		0-3		0-3		1-3
-	 *  groups:	{0-1},{1-3}	{0-2},{2-3}	{1-3},{0-1}	{2-3},{0-2}
-	 *
-	 * NUMA-1	0-1		0-2		1-3		2-3
-	 *  groups:	{0},{1}		{1},{2},{0}	{2},{3},{1}	{3},{2}
-	 *
-	 * NUMA-0	0		1		2		3
-	 *
-	 * The NUMA-2 groups for nodes 0 and 3 are obviously buggered, as the
-	 * group span isn't a subset of the domain span.
-	 */
-	WARN_ONCE(numa_distance > 2, "Shortest NUMA path spans too many nodes\n");
-
 	sched_domain_debug(sd, cpu);
 
 	rq_attach_root(rq, rd);
-- 
2.27.0