Re: [PATCH 3/8] x86/itmt: Move the "sched_itmt_enabled" sysctl to debugfs

[Tim Chen <tim.c.chen@linux.intel.com>]

On Wed, 2024-12-11 at 18:55 +0000, K Prateek Nayak wrote:
> "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.
> 

Valid values of setting "sched_itmt_enabled" likewise change from "1" or "0"
to "Y" or "N". 

> 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@infradead.org>
> Signed-off-by: K Prateek Nayak <kprateek.nayak@amd.com>

Reviewed-by: Tim Chen <tim.c.chen@linux.intel.com>

Tim

> ---
>  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 */