Re: [PATCH v7 1/2] nohz: add tick_nohz_full_add_cpus_to() and _remove_cpus_from() APIs

[Frederic Weisbecker <fweisbec@gmail.com>]

On Fri, Apr 10, 2015 at 04:53:51PM -0400, Chris Metcalf wrote:
> The "removes_cpus_from" API is useful, for example, to modify a cpumask
> to avoid the nohz cores so that interrupts aren't sent to them.
> 
> Likewise the "add_cpus_to" API is useful to modify a cpumask indicating
> some special nohz-type functionality so that the nohz cores are
> automatically added to that set.
> 
> Signed-off-by: Chris Metcalf <cmetcalf@ezchip.com>
> ---
> v7: no change here, just in part 2/2.
> 
> v6: I think we may finally have accessor names that are OK
> 
> v5: (skipped this patch)
> 
> v4: update accessor names to make them clearer [PeterZ]
> 
> v3: no change here, just in part 2/2.
> 
> v2: put the "...set_cpus" API together with the change to
> init_sched_domains() so that they can go into the timer tree
> independently of other changes in my tree.
> 
>  include/linux/tick.h | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
>  include/linux/tick.h | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> diff --git a/include/linux/tick.h b/include/linux/tick.h
> index 9c085dc12ae9..8d1754c0f694 100644
> --- a/include/linux/tick.h
> +++ b/include/linux/tick.h
> @@ -186,6 +186,18 @@ static inline bool tick_nohz_full_cpu(int cpu)
>  	return cpumask_test_cpu(cpu, tick_nohz_full_mask);
>  }
>  
> +static inline void tick_nohz_full_add_cpus_to(struct cpumask *mask)
> +{
> +	if (tick_nohz_full_enabled())
> +		cpumask_or(mask, mask, tick_nohz_full_mask);
> +}
> +
> +static inline void tick_nohz_full_remove_cpus_from(struct cpumask *mask)
> +{
> +	if (tick_nohz_full_enabled())
> +		cpumask_andnot(mask, mask, tick_nohz_full_mask);

I would prefer that you don't introduce new APIs if they aren't used in your
patchset. It seems that's the case for tick_nohz_full_remove_cpus_from().

Also we have housekeeping_affine() that affines a task to CPUs outside the
range of nohz full. In case you still need tick_nohz_full_remove_cpus_from()
in a further patchset, housekeeping_affine_cpumask() would extend the existing
naming.

> +}
> +
>  extern void __tick_nohz_full_check(void);
>  extern void tick_nohz_full_kick(void);
>  extern void tick_nohz_full_kick_cpu(int cpu);
> @@ -194,6 +206,8 @@ extern void __tick_nohz_task_switch(struct task_struct *tsk);
>  #else
>  static inline bool tick_nohz_full_enabled(void) { return false; }
>  static inline bool tick_nohz_full_cpu(int cpu) { return false; }
> +static inline void tick_nohz_full_add_cpus_to(struct cpumask *mask) { }
> +static inline void tick_nohz_full_remove_cpus_from(struct cpumask *mask) { }
>  static inline void __tick_nohz_full_check(void) { }
>  static inline void tick_nohz_full_kick_cpu(int cpu) { }
>  static inline void tick_nohz_full_kick(void) { }
> -- 
> 2.1.2
>