linux-kernel - [PATCH 3/8] x86/itmt: Move the "sched_itmt

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Message-ID: <20241211185552.4553-4-kprateek.nayak@amd.com>
Date: Wed, 11 Dec 2024 18:55:46 +0000
From: K Prateek Nayak <kprateek.nayak@....com>
To: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
	Peter Zijlstra <peterz@...radead.org>, Juri Lelli <juri.lelli@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>, <x86@...nel.org>,
	<linux-kernel@...r.kernel.org>
CC: "H. Peter Anvin" <hpa@...or.com>, Dietmar Eggemann
	<dietmar.eggemann@....com>, Steven Rostedt <rostedt@...dmis.org>, Ben Segall
	<bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>, Valentin Schneider
	<vschneid@...hat.com>, "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>, Tim Chen
	<tim.c.chen@...ux.intel.com>, Mario Limonciello <mario.limonciello@....com>,
	Meng Li <li.meng@....com>, Huang Rui <ray.huang@....com>, "Gautham R. Shenoy"
	<gautham.shenoy@....com>, K Prateek Nayak <kprateek.nayak@....com>
Subject: [PATCH 3/8] x86/itmt: Move the "sched_itmt_enabled" sysctl to debugfs

"sched_itmt_enabled" was only introduced as a debug toggle for any funky
ITMT behavior. Move the sysctl controlled from
"/proc/sys/kernel/sched_itmt_enabled" to debugfs at
"/sys/kernel/debug/x86/sched_itmt_enabled" with a notable change that a
cat on the file will return "Y" or "N" instead of "1" or "0" to
indicate that feature is enabled or disabled respectively.

Since ITMT is x86 specific (and PowerPC uses SD_ASYM_PACKING too), the
toggle was moved to "/sys/kernel/debug/x86/" as opposed to
"/sys/kernel/debug/sched/"

Suggested-by: Peter Zijlstra <peterz@...radead.org>
Signed-off-by: K Prateek Nayak <kprateek.nayak@....com>
---
 arch/x86/kernel/itmt.c | 56 ++++++++++++++++++++----------------------
 1 file changed, 27 insertions(+), 29 deletions(-)

diff --git a/arch/x86/kernel/itmt.c b/arch/x86/kernel/itmt.c
index ee43d1bd41d0..9cea1fc36c18 100644
--- a/arch/x86/kernel/itmt.c
+++ b/arch/x86/kernel/itmt.c
@@ -19,6 +19,7 @@
 #include <linux/sched.h>
 #include <linux/cpumask.h>
 #include <linux/cpuset.h>
+#include <linux/debugfs.h>
 #include <linux/mutex.h>
 #include <linux/sysctl.h>
 #include <linux/nodemask.h>
@@ -34,45 +35,38 @@ static bool __read_mostly sched_itmt_capable;
  * of higher turbo frequency for cpus supporting Intel Turbo Boost Max
  * Technology 3.0.
  *
- * It can be set via /proc/sys/kernel/sched_itmt_enabled
+ * It can be set via /sys/kernel/debug/x86/sched_itmt_enabled
  */
 bool __read_mostly sysctl_sched_itmt_enabled;
 
-static int sched_itmt_update_handler(const struct ctl_table *table, int write,
-				     void *buffer, size_t *lenp, loff_t *ppos)
+static ssize_t sched_itmt_enabled_write(struct file *filp,
+					const char __user *ubuf,
+					size_t cnt, loff_t *ppos)
 {
-	unsigned int old_sysctl;
-	int ret;
+	ssize_t result;
+	bool orig;
 
 	guard(mutex)(&itmt_update_mutex);
 
-	if (!sched_itmt_capable)
-		return -EINVAL;
-
-	old_sysctl = sysctl_sched_itmt_enabled;
-	ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
+	orig = sysctl_sched_itmt_enabled;
+	result = debugfs_write_file_bool(filp, ubuf, cnt, ppos);
 
-	if (!ret && write && old_sysctl != sysctl_sched_itmt_enabled) {
+	if (sysctl_sched_itmt_enabled != orig) {
 		x86_topology_update = true;
 		rebuild_sched_domains();
 	}
 
-	return ret;
+	return result;
 }
 
-static struct ctl_table itmt_kern_table[] = {
-	{
-		.procname	= "sched_itmt_enabled",
-		.data		= &sysctl_sched_itmt_enabled,
-		.maxlen		= sizeof(unsigned int),
-		.mode		= 0644,
-		.proc_handler	= sched_itmt_update_handler,
-		.extra1		= SYSCTL_ZERO,
-		.extra2		= SYSCTL_ONE,
-	},
+static const struct file_operations dfs_sched_itmt_fops = {
+	.read =         debugfs_read_file_bool,
+	.write =        sched_itmt_enabled_write,
+	.open =         simple_open,
+	.llseek =       default_llseek,
 };
 
-static struct ctl_table_header *itmt_sysctl_header;
+static struct dentry *dfs_sched_itmt;
 
 /**
  * sched_set_itmt_support() - Indicate platform supports ITMT
@@ -98,9 +92,15 @@ int sched_set_itmt_support(void)
 	if (sched_itmt_capable)
 		return 0;
 
-	itmt_sysctl_header = register_sysctl("kernel", itmt_kern_table);
-	if (!itmt_sysctl_header)
+	dfs_sched_itmt = debugfs_create_file_unsafe("sched_itmt_enabled",
+						    0644,
+						    arch_debugfs_dir,
+						    &sysctl_sched_itmt_enabled,
+						    &dfs_sched_itmt_fops);
+	if (IS_ERR_OR_NULL(dfs_sched_itmt)) {
+		dfs_sched_itmt = NULL;
 		return -ENOMEM;
+	}
 
 	sched_itmt_capable = true;
 
@@ -131,10 +131,8 @@ void sched_clear_itmt_support(void)
 
 	sched_itmt_capable = false;
 
-	if (itmt_sysctl_header) {
-		unregister_sysctl_table(itmt_sysctl_header);
-		itmt_sysctl_header = NULL;
-	}
+	debugfs_remove(dfs_sched_itmt);
+	dfs_sched_itmt = NULL;
 
 	if (sysctl_sched_itmt_enabled) {
 		/* disable sched_itmt if we are no longer ITMT capable */
-- 
2.34.1