Re: [PATCH 13/25] context_tracking: Introduce context_tracking_enabled_cpu()

Peter Zijlstra
2018-11-20T14:03:21Z

On Wed, Nov 14, 2018 at 03:45:57AM +0100, Frederic Weisbecker wrote:
> This allows us to check if a remote CPU runs context tracking
> (ie: is nohz_full). We'll need that to reliably support "nice"
> accounting on kcpustat.
>
> Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
> Cc: Yauheni Kaliuta <yauheni.kaliuta@redhat.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Rik van Riel <riel@redhat.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Wanpeng Li <wanpengli@tencent.com>
> Cc: Ingo Molnar <mingo@kernel.org>
> ---
> include/linux/context_tracking_state.h | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/include/linux/context_tracking_state.h b/include/linux/context_tracking_state.h
> index 08f125f..5877177 100644
> --- a/include/linux/context_tracking_state.h
> +++ b/include/linux/context_tracking_state.h
> @@ -31,6 +31,11 @@ static inline bool context_tracking_enabled(void)
> return static_branch_unlikely(&context_tracking_key);
> }
>
> +static inline bool context_tracking_enabled_cpu(int cpu)
> +{
> + return per_cpu(context_tracking.active, cpu);
> +}
> +
> static inline bool context_tracking_enabled_this_cpu(void)
> {
> return __this_cpu_read(context_tracking.active);

Should not the last two be something like:

static inline bool context_tracking_enabled_cpu(int cpu)
{
return context_tracking_enabled() && per_cpu(context_tracking.active, cpu);
}

static inline bool context_tracking_enabled_this_cpu(void)
{
return context_tracking_enabled() && __this_cpu_read(context_tracking.active);
}

Because, afaict, not all callsites first check the static key.