Re: [PATCH v3 14/20] sched/debug: Provide debugfs to enable/disable steal monitor

[Ilya Leoshkevich <iii@linux.ibm.com>]

On 5/14/26 17:21, Shrikanth Hegde wrote:
> Add a debugfs "enable" file to enable steal time monitor.
> 
> Computing steal time and acting on it periodically are to be opted by
> the user. This helps to avoid any overhead when the feature
> is disabled.
> 
> It is disabled by default.
> 
> Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
> ---
>   kernel/sched/core.c  |  1 +
>   kernel/sched/debug.c | 29 +++++++++++++++++++++++++++++
>   kernel/sched/sched.h |  2 ++
>   3 files changed, 32 insertions(+)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 0d1995c65ce6..1533a44d1a6b 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c

[...]

> @@ -592,6 +592,33 @@ static void debugfs_ext_server_init(void)
>   #endif /* CONFIG_SCHED_CLASS_EXT */
>   
>   #ifdef CONFIG_PREFERRED_CPU
> +__read_mostly bool sched_sm_wr_enable;
> +
> +static ssize_t sched_sm_en_write(struct file *filp, const char __user *ubuf,
> +				 size_t cnt, loff_t *ppos)
> +{
> +	bool orig = sched_sm_wr_enable;
> +	ssize_t result;
> +
> +	result = debugfs_write_file_bool(filp, ubuf, cnt, ppos);
> +
> +	if (sched_sm_wr_enable && !orig) {
> +		static_branch_enable(&__sched_sm_enable);

Would it make sense to clear the steal monitor state when enabling it?
Otherwise we may immediately trigger a bogus "dec" if user did a disable
during contention and re-enabled when everything is quiet.

[...]