linux-kernel - [PATCH] sched/topology: Enable topology_span

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Message-Id: <1729619853-2597-1-git-send-email-ssengar@linux.microsoft.com>
Date: Tue, 22 Oct 2024 10:57:33 -0700
From: Saurabh Sengar <ssengar@...ux.microsoft.com>
To: mingo@...hat.com,
	peterz@...radead.org,
	juri.lelli@...hat.com,
	vincent.guittot@...aro.org,
	dietmar.eggemann@....com,
	rostedt@...dmis.org,
	bsegall@...gle.com,
	mgorman@...e.de,
	vschneid@...hat.com,
	linux-kernel@...r.kernel.org
Cc: stable@...r.kernel.org,
	ssengar@...rosoft.com,
	srivatsa@...il.mit.edu
Subject: [PATCH] sched/topology: Enable topology_span_sane check only for debug builds

On a x86 system under test with 1780 CPUs, topology_span_sane() takes
around 8 seconds cumulatively for all the iterations. It is an expensive
operation which does the sanity of non-NUMA topology masks.

CPU topology is not something which changes very frequently hence make
this check optional for the systems where the topology is trusted and
need faster bootup.

Restrict this to SCHED_DEBUG builds so that this penalty can be avoided
for the systems who wants to avoid it.

Fixes: ccf74128d66c ("sched/topology: Assert non-NUMA topology masks don't (partially) overlap")
Signed-off-by: Saurabh Sengar <ssengar@...ux.microsoft.com>
---
 kernel/sched/topology.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index 9748a4c8d668..dacc8c6f978b 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -2354,6 +2354,7 @@ static struct sched_domain *build_sched_domain(struct sched_domain_topology_leve
 	return sd;
 }
 
+#ifdef CONFIG_SCHED_DEBUG
 /*
  * Ensure topology masks are sane, i.e. there are no conflicts (overlaps) for
  * any two given CPUs at this (non-NUMA) topology level.
@@ -2387,6 +2388,7 @@ static bool topology_span_sane(struct sched_domain_topology_level *tl,
 
 	return true;
 }
+#endif
 
 /*
  * Build sched domains for a given set of CPUs and attach the sched domains
@@ -2417,8 +2419,10 @@ build_sched_domains(const struct cpumask *cpu_map, struct sched_domain_attr *att
 		sd = NULL;
 		for_each_sd_topology(tl) {
 
+#ifdef CONFIG_SCHED_DEBUG
 			if (WARN_ON(!topology_span_sane(tl, cpu_map, i)))
 				goto error;
+#endif
 
 			sd = build_sched_domain(tl, cpu_map, attr, sd, i);
 
-- 
2.43.0