Re: [PATCH v2] credit: generalize __vcpu_has_soft_affinity()

[George Dunlap <george.dunlap@eu.citrix.com>]

On 03/06/2015 07:36 AM, Jan Beulich wrote:
> As pointed out in the discussion of the patch at
> http://lists.xenproject.org/archives/html/xen-devel/2015-02/msg03256.html 
> generalizing the conditions here means code elsewhere doesn't need to
> take into consideration internals of how load balancing in the credit
> scheduler works.
> 
> Signed-off-by: Jan Beulich <jbeulich@suse.com>
> ---
> v2: Use VCPU2ONLINE(vc) (or really an open coded variant thereof)
>     instead of cpu_online_map (suggested by Dario).
> 
> --- a/xen/common/sched_credit.c
> +++ b/xen/common/sched_credit.c
> @@ -292,11 +292,10 @@ __runq_remove(struct csched_vcpu *svc)
>  static inline int __vcpu_has_soft_affinity(const struct vcpu *vc,
>                                             const cpumask_t *mask)
>  {
> -    if ( cpumask_full(vc->cpu_soft_affinity)
> -         || !cpumask_intersects(vc->cpu_soft_affinity, mask) )
> -        return 0;
> -
> -    return 1;
> +    return !cpumask_subset(cpupool_online_cpumask(vc->domain->cpupool),
> +                           vc->cpu_soft_affinity) &&
> +           !cpumask_subset(vc->cpu_soft_affinity, vc->cpu_hard_affinity) &&
> +           cpumask_intersects(vc->cpu_soft_affinity, mask);

It looks like the comment above this line could use changing too; perhaps:

---
Hard affinity balancing is always necessary and must never be skipped.
But soft affinity need only be considered when it has a functionally
different effect than other constraints (such as hard affinity, cpus
online, or cpupools).

Soft affinity only needs to be considered if:
* The cpus in the cpupool are not a subset of soft affinity
* The hard affinity is not a subset of soft affinity
* There is an overlap between the soft affinity and the mask which is
currently being considered.
---

With the comment updated:

Reviewed-by: George Dunlap <george.dunlap@eu.citrix.com>