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Date:   Tue, 8 Nov 2022 15:30:46 +0530
From:   Vishal Chourasia <vishalc@linux.vnet.ibm.com>
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-kernel@vger.kernel.org, mingo@redhat.com,
        vincent.guittot@linaro.org, vschneid@redhat.com,
        srikar@linux.vnet.ibm.com, sshegde@linux.ibm.com,
        linuxppc-dev@lists.ozlabs.org, ritesh.list@gmail.com,
        aneesh.kumar@linux.ibm.com
Subject: Re: sched/debug: CPU hotplug operation suffers in a large cpu systems
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Thanks Greg & Peter for your direction.=20

While we pursue the idea of having debugfs based on kernfs, we thought about
having a boot time parameter which would disable creating and updating of t=
he
sched_domain debugfs files and this would also be useful even when the kern=
fs
solution kicks in, as users who may not care about these debugfs files would
benefit from a faster CPU hotplug operation.

However, these sched_domain debugfs files are created by default.

-- vishal.c

------>8-----------------------------------------------------8<------------=
--

=46rom f66f66ee05a9f719b58822d13e501d65391dd9d3 Mon Sep 17 00:00:00 2001
=46rom: Vishal Chourasia <vishalc@linux.vnet.ibm.com>
Date: Tue, 8 Nov 2022 14:21:15 +0530
Subject: [PATCH] Add kernel parameter to disable creation of sched_domain
 files

For large systems, creation of sched_domain debug files takes unusually long
time. In which case, sched_sd_export can be passed as kernel command line
parameter during boot time to prevent kernel from creating sched_domain fil=
es.

This commit adds a kernel command line parameter, sched_sd_export, which ca=
n be
used to, optionally, disable the creation of sched_domain debug files.=20
---
 kernel/sched/debug.c    |  9 ++++++---
 kernel/sched/sched.h    |  1 +
 kernel/sched/topology.c | 11 ++++++++++-
 3 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index bb3d63bdf4ae..bd307847b76a 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -279,6 +279,7 @@ static const struct file_operations sched_dynamic_fops =
=3D {
 #endif /* CONFIG_PREEMPT_DYNAMIC */
=20
 __read_mostly bool sched_debug_verbose;
+__read_mostly int sched_debug_export =3D 1;
=20
 static const struct seq_operations sched_debug_sops;
=20
@@ -321,9 +322,11 @@ static __init int sched_init_debug(void)
 	debugfs_create_u32("migration_cost_ns", 0644, debugfs_sched, &sysctl_sche=
d_migration_cost);
 	debugfs_create_u32("nr_migrate", 0644, debugfs_sched, &sysctl_sched_nr_mi=
grate);
=20
-	mutex_lock(&sched_domains_mutex);
-	update_sched_domain_debugfs();
-	mutex_unlock(&sched_domains_mutex);
+	if (likely(sched_debug_export)) {
+		mutex_lock(&sched_domains_mutex);
+		update_sched_domain_debugfs();
+		mutex_unlock(&sched_domains_mutex);
+	}
 #endif
=20
 #ifdef CONFIG_NUMA_BALANCING
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index e26688d387ae..a4d06588d876 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2738,6 +2738,7 @@ extern struct sched_entity *__pick_last_entity(struct=
 cfs_rq *cfs_rq);
=20
 #ifdef	CONFIG_SCHED_DEBUG
 extern bool sched_debug_verbose;
+extern int sched_debug_export;
=20
 extern void print_cfs_stats(struct seq_file *m, int cpu);
 extern void print_rt_stats(struct seq_file *m, int cpu);
diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index 8739c2a5a54e..7bcdbc2f856d 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -19,6 +19,13 @@ static int __init sched_debug_setup(char *str)
 }
 early_param("sched_verbose", sched_debug_setup);
=20
+static int __init sched_debug_disable_export(char *str)
+{
+	sched_debug_export =3D 0;
+	return 0;
+}
+early_param("sched_sd_export", sched_debug_disable_export);
+
 static inline bool sched_debug(void)
 {
 	return sched_debug_verbose;
@@ -152,6 +159,7 @@ static void sched_domain_debug(struct sched_domain *sd,=
 int cpu)
 #else /* !CONFIG_SCHED_DEBUG */
=20
 # define sched_debug_verbose 0
+# define sched_debug_export 1
 # define sched_domain_debug(sd, cpu) do { } while (0)
 static inline bool sched_debug(void)
 {
@@ -2632,7 +2640,8 @@ void partition_sched_domains_locked(int ndoms_new, cp=
umask_var_t doms_new[],
 	dattr_cur =3D dattr_new;
 	ndoms_cur =3D ndoms_new;
=20
-	update_sched_domain_debugfs();
+	if (likely(sched_debug_export))
+		update_sched_domain_debugfs();
 }
=20
 /*

base-commit: 7e18e42e4b280c85b76967a9106a13ca61c16179
--=20
2.31.1

 =20

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