Re: [PATCH v5 02/12] x86/paravirt: switch time pvops functions to use static_call()

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 3/8/21 7:28 AM, Juergen Gross wrote:
> --- a/arch/x86/xen/time.c
> +++ b/arch/x86/xen/time.c
> @@ -379,11 +379,6 @@ void xen_timer_resume(void)
>       }
>  }
>  
> -static const struct pv_time_ops xen_time_ops __initconst = {
> -     .sched_clock = xen_sched_clock,
> -     .steal_clock = xen_steal_clock,
> -};
> -
>  static struct pvclock_vsyscall_time_info *xen_clock __read_mostly;
>  static u64 xen_clock_value_saved;
>  
> @@ -528,7 +523,8 @@ static void __init xen_time_init(void)
>  void __init xen_init_time_ops(void)
>  {
>       xen_sched_clock_offset = xen_clocksource_read();
> -     pv_ops.time = xen_time_ops;
> +     static_call_update(pv_steal_clock, xen_steal_clock);
> +     paravirt_set_sched_clock(xen_sched_clock);
>  
>       x86_init.timers.timer_init = xen_time_init;
>       x86_init.timers.setup_percpu_clockev = x86_init_noop;
> @@ -570,7 +566,8 @@ void __init xen_hvm_init_time_ops(void)
>       }
>  
>       xen_sched_clock_offset = xen_clocksource_read();
> -     pv_ops.time = xen_time_ops;
> +     static_call_update(pv_steal_clock, xen_steal_clock);
> +     paravirt_set_sched_clock(xen_sched_clock);
>       x86_init.timers.setup_percpu_clockev = xen_time_init;
>       x86_cpuinit.setup_percpu_clockev = xen_hvm_setup_cpu_clockevents;


There is a bunch of stuff that's common between the two cases so it can be 
factored out.


>  
> diff --git a/drivers/xen/time.c b/drivers/xen/time.c
> index 108edbcbc040..152dd33bb223 100644
> --- a/drivers/xen/time.c
> +++ b/drivers/xen/time.c
> @@ -7,6 +7,7 @@
>  #include <linux/math64.h>
>  #include <linux/gfp.h>
>  #include <linux/slab.h>
> +#include <linux/static_call.h>
>  
>  #include <asm/paravirt.h>
>  #include <asm/xen/hypervisor.h>
> @@ -175,7 +176,7 @@ void __init xen_time_setup_guest(void)
>       xen_runstate_remote = !HYPERVISOR_vm_assist(VMASST_CMD_enable,
>                                       VMASST_TYPE_runstate_update_flag);
>  
> -     pv_ops.time.steal_clock = xen_steal_clock;
> +     static_call_update(pv_steal_clock, xen_steal_clock);
>  


Do we actually need this? We've already set this up in xen_init_time_ops(). 
(But maybe for ARM).


-boris


>       static_key_slow_inc(&paravirt_steal_enabled);
>       if (xen_runstate_remote)