Re: [Xen-devel] [PATCH v2 09/48] xen/sched: move some per-vcpu items to struct sched_unit

[Jan Beulich <jbeulich@xxxxxxxx>]

On 09.08.2019 16:57, Juergen Gross wrote:
> V2:
> - move affinity_broken back to struct vcpu (Jan Beulich)

But this alone won't work: Now a 2nd vCPU in a unit will clobber
what a 1st one may have set as an affinity override. I don't
think you can get away without a per-vCPU CPU mask, or a
combination of per-vCPU and per-unit state flags.

> @@ -971,26 +986,29 @@ static int cpu_disable_scheduler_check(unsigned int cpu)
>  void sched_set_affinity(
>      struct vcpu *v, const cpumask_t *hard, const cpumask_t *soft)
>  {
> -    sched_adjust_affinity(dom_scheduler(v->domain), v->sched_unit, hard, 
> soft);
> +    struct sched_unit *unit = v->sched_unit;
> +
> +    sched_adjust_affinity(dom_scheduler(unit->domain), unit, hard, soft);

In a situation like this I think it would be better to use
v->domain (I don't think you mean to remove struct vcpu's field).
v has just been de-referenced, so v->domain being in cache is
more likely than unit->domain, and there's then also no data
dependency of the second load on the first one.

Jan

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