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

[Ilya Leoshkevich]

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@xxxxxxxxxxxxx>
> ---
>   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
> @@ -11270,6 +11270,7 @@ void sched_change_end(struct sched_change_ctx *ctx)
>   #ifdef CONFIG_PREFERRED_CPU
>   /* npc - non preferred CPU */
>   static DEFINE_PER_CPU(struct cpu_stop_work, npc_push_task_work);
> +DEFINE_STATIC_KEY_FALSE(__sched_sm_enable);
>   
>   static int sched_non_preferred_cpu_push_stop(void *arg)
>   {
> diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
> index b1abfdc168bf..be8d223b43fd 100644
> --- a/kernel/sched/debug.c
> +++ b/kernel/sched/debug.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);
> +	} else if (!sched_sm_wr_enable && orig) {
> +		static_branch_disable(&__sched_sm_enable);
> +		cpumask_copy(&__cpu_preferred_mask, cpu_online_mask);
> +	}

What if two userspace processes write to this debugfs file concurrently?
I think __sched_sm_enable and __cpu_preferred_mask may go out of sync.

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