Re: [Xen-devel] [PATCH 02/13] xen/events: remove unnecessary init_evtchn_cpu_bindings()

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Fri, Sep 13, 2013 at 05:59:50PM +0100, David Vrabel wrote:
> From: David Vrabel <david.vrabel@xxxxxxxxxx>
> 
> Event channels are always explicitly bound to a specific VCPU before
> they are first enabled.  There is no need to initialize all possible
> events as bound to VCPU 0 at start of day or after a resume.

How long has this presumption about explicit bounding been in the
hypervisor?

Should there also be a patch in the Xen headers documenting this
behavior?

Looks good to me - thought I would add the comment mentioning how
long this behavior has been with the hypervisor - as we still can
run on Xen 4.0 hypervisors and should not break that (and perhaps
they don't rebind there?).

> 
> Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>
> ---
>  drivers/xen/events.c |   22 ----------------------
>  1 files changed, 0 insertions(+), 22 deletions(-)
> 
> diff --git a/drivers/xen/events.c b/drivers/xen/events.c
> index ddcdbb5..1e2c74b 100644
> --- a/drivers/xen/events.c
> +++ b/drivers/xen/events.c
> @@ -334,24 +334,6 @@ static void bind_evtchn_to_cpu(unsigned int chn, 
> unsigned int cpu)
>       info_for_irq(irq)->cpu = cpu;
>  }
>  
> -static void init_evtchn_cpu_bindings(void)
> -{
> -     int i;
> -#ifdef CONFIG_SMP
> -     struct irq_info *info;
> -
> -     /* By default all event channels notify CPU#0. */
> -     list_for_each_entry(info, &xen_irq_list_head, list) {
> -             struct irq_desc *desc = irq_to_desc(info->irq);
> -             cpumask_copy(desc->irq_data.affinity, cpumask_of(0));
> -     }
> -#endif
> -
> -     for_each_possible_cpu(i)
> -             memset(per_cpu(cpu_evtchn_mask, i),
> -                    (i == 0) ? ~0 : 0, NR_EVENT_CHANNELS/8);
> -}
> -
>  static inline void clear_evtchn(int port)
>  {
>       struct shared_info *s = HYPERVISOR_shared_info;
> @@ -1778,8 +1760,6 @@ void xen_irq_resume(void)
>       unsigned int cpu, evtchn;
>       struct irq_info *info;
>  
> -     init_evtchn_cpu_bindings();
> -
>       /* New event-channel space is not 'live' yet. */
>       for (evtchn = 0; evtchn < NR_EVENT_CHANNELS; evtchn++)
>               mask_evtchn(evtchn);
> @@ -1890,8 +1870,6 @@ void __init xen_init_IRQ(void)
>       for (i = 0; i < NR_EVENT_CHANNELS; i++)
>               evtchn_to_irq[i] = -1;
>  
> -     init_evtchn_cpu_bindings();
> -
>       /* No event channels are 'live' right now. */
>       for (i = 0; i < NR_EVENT_CHANNELS; i++)
>               mask_evtchn(i);
> -- 
> 1.7.2.5
> 

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