Re: [RFC PATCH v2 12/17] sched: A quick and dirty cgroup tagging interface

[Peter Zijlstra]

On Thu, Apr 25, 2019 at 10:26:53AM -0400, Phil Auld wrote:
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index e8e5f26db052..b312ea1e28a4 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -7541,6 +7541,9 @@ static int cpu_core_tag_write_u64(struct cgroup_subsys_state *css, struct cftype
>         if (val > 1)
>                 return -ERANGE;
>  
> +       if (num_online_cpus() <= 1) 
> +               return -EINVAL;

We actually know if there SMT on the system or not, which is much better
indication still:

	if (!static_branch_likely(&sched_smt_present))
		return -EINVAL;

>         if (tg->tagged == !!val)
>                 return 0;
>  
> 
> 
> 
> --