linux-kernel - [PATCH v2] sched/topology: Enable topology_span

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Message-Id: <1731922777-7121-1-git-send-email-ssengar@linux.microsoft.com>
Date: Mon, 18 Nov 2024 01:39:37 -0800
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 v2] 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_verbose kernel cmdline option so that this penalty
can be avoided for the systems who wants to avoid it.

Cc: stable@...r.kernel.org
Fixes: ccf74128d66c ("sched/topology: Assert non-NUMA topology masks don't (partially) overlap")
Signed-off-by: Saurabh Sengar <ssengar@...ux.microsoft.com>
---
[V2]
	- Use kernel cmdline param instead of compile time flag.

 kernel/sched/topology.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index 9748a4c8d668..4ca63bff321d 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -2363,6 +2363,13 @@ static bool topology_span_sane(struct sched_domain_topology_level *tl,
 {
 	int i = cpu + 1;
 
+	/* Skip the topology sanity check for non-debug, as it is a time-consuming operatin */
+	if (!sched_debug_verbose) {
+		pr_info_once("%s: Skipping topology span sanity check. Use `sched_verbose` boot parameter to enable it.\n",
+			     __func__);
+		return true;
+	}
+
 	/* NUMA levels are allowed to overlap */
 	if (tl->flags & SDTL_OVERLAP)
 		return true;
-- 
2.43.0