Re: [Xen-devel] [PATCH] xen/sched: Introduce domain_vcpu() helper

[Julien Grall <julien.grall@xxxxxxx>]

Hi,

On 23/01/2019 14:59, Andrew Cooper wrote:
> +/*
> + * For each allocated vcpu, d->vcpu[X]->vcpu_id == X
> + *
> + * During construction, all vcpus in d->vcpu[] are allocated sequentially, and
> + * in ascending order.  Therefore, if d->vcpu[N] exists (e.g. derived from
> + * current), all vcpus with an id less than N also exist.
> + *
> + * SMP considerations: The idle domain is constructed before APs are started.
> + * All other domains have d->vcpu[] allocated and d->max_vcpus set before the
> + * domain is made visible in the domlist, which is serialised on the global
> + * domlist_update_lock.
> + *
> + * Therefore, all observations of d->max_vcpus vs d->vcpu[] will be consistent
> + * despite the lack of smp_* barriers, either by being on the same CPU as the
> + * one which issued the writes, or because of barrier properties of the domain
> + * having been inserted into the domlist.
> + */
From an Arm perspective, this makes sense to me.

Cheers,

--
Julien Grall

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