Re: [Xen-devel] [PATCH 5/5] xen: sched: simplify ACPI S3 resume path.

[George Dunlap <George.Dunlap@xxxxxxxxxxxxx>]

On Tue, Jan 17, 2017 at 5:27 PM, Dario Faggioli
<dario.faggioli@xxxxxxxxxx> wrote:
> In fact, when domains are being unpaused:
>  - it's not necessary to put the vcpu to sleep, as
>    they are all already paused;
>  - it is not necessary to call vcpu_migrate(), as
>    the vcpus are still paused, and therefore won't
>    wakeup anyway.
>
> Basically, the only important thing is to call
> pick_cpu, to let the scheduler run and figure out
> what would be the best initial placement (i.e., the
> value stored in v->processor), for the vcpus, as
> they come back up, one after another.
>
> Note that this is consistent with what was happening
> before this change, as vcpu_migrate() calls pick_cpu.
> But much simpler and quicker.
>
> Signed-off-by: Dario Faggioli <dario.faggioli@xxxxxxxxxx>

Reviewed-by: George Dunlap <george.dunlap@xxxxxxxxxx>

> ---
> Cc: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
> ---
>  xen/common/schedule.c |   22 ++++++++++------------
>  1 file changed, 10 insertions(+), 12 deletions(-)
>
> diff --git a/xen/common/schedule.c b/xen/common/schedule.c
> index bee5d1f..43b5b99 100644
> --- a/xen/common/schedule.c
> +++ b/xen/common/schedule.c
> @@ -635,7 +635,11 @@ void restore_vcpu_affinity(struct domain *d)
>
>      for_each_vcpu ( d, v )
>      {
> -        spinlock_t *lock = vcpu_schedule_lock_irq(v);
> +        spinlock_t *lock;
> +
> +        ASSERT(!vcpu_runnable(v));
> +
> +        lock = vcpu_schedule_lock_irq(v);
>
>          if ( v->affinity_broken )
>          {
> @@ -659,17 +663,11 @@ void restore_vcpu_affinity(struct domain *d)
>                      cpupool_domain_cpumask(v->domain));
>          v->processor = cpumask_any(cpumask_scratch_cpu(cpu));
>
> -        if ( v->processor == cpu )
> -        {
> -            set_bit(_VPF_migrating, &v->pause_flags);
> -            spin_unlock_irq(lock);;
> -            vcpu_sleep_nosync(v);
> -            vcpu_migrate(v);
> -        }
> -        else
> -        {
> -            spin_unlock_irq(lock);
> -        }
> +        spin_unlock_irq(lock);;
> +
> +        lock = vcpu_schedule_lock_irq(v);
> +        v->processor = SCHED_OP(VCPU2OP(v), pick_cpu, v);
> +        spin_unlock_irq(lock);
>      }
>
>      domain_update_node_affinity(d);
>
>
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