Re: [PATCH v2 20/23] sched/cache: Add user control to adjust the parameters of cache-aware scheduling

[Peter Zijlstra]

On Wed, Dec 03, 2025 at 03:07:39PM -0800, Tim Chen wrote:

> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 466ba8b7398c..95bf080bbbf0 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -2436,9 +2436,11 @@ extern void migrate_enable(void);
>  DEFINE_LOCK_GUARD_0(migrate, migrate_disable(), migrate_enable())
>  
>  #ifdef CONFIG_SCHED_CACHE
> +DECLARE_STATIC_KEY_FALSE(sched_cache_on);
> +
>  static inline bool sched_cache_enabled(void)
>  {
> -	return false;
> +	return static_branch_unlikely(&sched_cache_on);
>  }
>  #endif
>  
> diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
> index 02e16b70a790..cde324672103 100644
> --- a/kernel/sched/debug.c
> +++ b/kernel/sched/debug.c
> @@ -169,6 +169,53 @@ static const struct file_operations sched_feat_fops = {
>  	.release	= single_release,
>  };
>  
> +#ifdef CONFIG_SCHED_CACHE
> +#define SCHED_CACHE_CREATE_CONTROL(name, max)			  \
> +static ssize_t sched_cache_write_##name(struct file *filp,	  \
> +					const char __user *ubuf,  \
> +					size_t cnt, loff_t *ppos) \
> +{								  \
> +	char buf[16];						  \
> +	unsigned int val;					  \
> +	if (cnt > 15)						  \
> +		cnt = 15;					  \
> +	if (copy_from_user(&buf, ubuf, cnt))			  \
> +		return -EFAULT;					  \
> +	buf[cnt] = '\0';					  \


> +	if (kstrtouint(buf, 10, &val))				  \
> +		return -EINVAL;					  \
> +	if (val > (max))						  \
> +		return -EINVAL;					  \
> +	llc_##name = val;					  \
> +	if (!strcmp(#name, "enabled"))				  \
> +		sched_cache_set(false);				  \

Oh gawd :-(

Please just write out all the various write methods and use
kstrtoul_from_user() and kstrtobool_from_user() where applicable.

> +	*ppos += cnt;						  \
> +	return cnt;						  \
> +}								  \
> +static int sched_cache_show_##name(struct seq_file *m, void *v)	  \
> +{								  \
> +	seq_printf(m, "%d\n", llc_##name);			  \
> +	return 0;						  \
> +}								  \
> +static int sched_cache_open_##name(struct inode *inode,		  \
> +				   struct file *filp)		  \
> +{								  \
> +	return single_open(filp, sched_cache_show_##name, NULL);  \
> +}								  \
> +static const struct file_operations sched_cache_fops_##name = {	  \
> +	.open		= sched_cache_open_##name,		  \
> +	.write		= sched_cache_write_##name,		  \
> +	.read		= seq_read,				  \
> +	.llseek		= seq_lseek,				  \
> +	.release	= single_release,			  \
> +}
> +
> +SCHED_CACHE_CREATE_CONTROL(overload_pct, 100);
> +SCHED_CACHE_CREATE_CONTROL(imb_pct, 100);
> +SCHED_CACHE_CREATE_CONTROL(aggr_tolerance, 100);
> +SCHED_CACHE_CREATE_CONTROL(enabled, 1);