Re: [Xen-devel] [PATCH v3 4/4] xen/arm: account for stolen ticks

[Marc Zyngier <marc.zyngier@xxxxxxx>]

Hi Stefano,

On 08/05/13 16:41, Stefano Stabellini wrote:
> Register the runstate_memory_area with the hypervisor.
> Use pv_time_ops.steal_clock to account for stolen ticks.
> 
> Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
> 
> Changes in v3:
> - use BUG_ON and smp_processor_id.
> ---
>  arch/arm/xen/enlighten.c |   22 ++++++++++++++++++++++
>  1 files changed, 22 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
> index 13609e0..dfa7738 100644
> --- a/arch/arm/xen/enlighten.c
> +++ b/arch/arm/xen/enlighten.c
> @@ -14,7 +14,10 @@
>  #include <xen/xen-ops.h>
>  #include <asm/xen/hypervisor.h>
>  #include <asm/xen/hypercall.h>
> +#include <asm/arch_timer.h>
>  #include <asm/system_misc.h>
> +#include <asm/paravirt.h>
> +#include <linux/jump_label.h>
>  #include <linux/interrupt.h>
>  #include <linux/irqreturn.h>
>  #include <linux/module.h>
> @@ -152,6 +155,19 @@ int xen_unmap_domain_mfn_range(struct vm_area_struct 
> *vma,
>  }
>  EXPORT_SYMBOL_GPL(xen_unmap_domain_mfn_range);
>  
> +unsigned long long xen_stolen_accounting(int cpu)
> +{
> +     struct vcpu_runstate_info state;
> +
> +     BUG_ON(cpu != smp_processor_id());
> +
> +     xen_get_runstate_snapshot(&state);
> +
> +     WARN_ON(state.state != RUNSTATE_running);
> +
> +     return state.time[RUNSTATE_runnable] + state.time[RUNSTATE_offline];
> +}
> +
>  static void __init xen_percpu_init(void *unused)
>  {
>       struct vcpu_register_vcpu_info info;
> @@ -169,6 +185,8 @@ static void __init xen_percpu_init(void *unused)
>       BUG_ON(err);
>       per_cpu(xen_vcpu, cpu) = vcpup;
>  
> +     xen_setup_runstate_info(cpu);
> +
>       enable_percpu_irq(xen_events_irq, 0);
>  }
>  
> @@ -300,6 +318,10 @@ static int __init xen_init_events(void)
>  
>       on_each_cpu(xen_percpu_init, NULL, 0);
>  
> +     pv_time_ops.steal_clock = xen_stolen_accounting;

What guarantee do we have that this is done before the rest of the
kernel calls paravirt_steal_clock()? What if we have Xen support enabled
but don't run as a Xen guest?

> +     static_key_slow_inc(&paravirt_steal_enabled);
> +     static_key_slow_inc(&paravirt_steal_rq_enabled);
> +
>       return 0;
>  }
>  postcore_initcall(xen_init_events);
> 

Thanks,

        M.
-- 
Jazz is not dead. It just smells funny...


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