Re: [PATCH 4/4] sched: Use the auto-generated list of schedulers

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 17/12/2015 20:59, Jonathan Creekmore wrote:
> Instead of having a manually-curated list of schedulers, use the array
> that was auto-generated simply by compiling in the scheduler files as
> the sole source of truth of the available schedulers.
>
> CC: George Dunlap <george.dunlap@eu.citrix.com>
> CC: Dario Faggioli <dario.faggioli@citrix.com>
> Signed-off-by: Jonathan Creekmore <jonathan.creekmore@gmail.com>
> ---
>  xen/common/schedule.c      | 24 +++++++-----------------
>  xen/include/xen/sched-if.h |  5 -----
>  2 files changed, 7 insertions(+), 22 deletions(-)
>
> diff --git a/xen/common/schedule.c b/xen/common/schedule.c
> index 2f98a48..efbd67d 100644
> --- a/xen/common/schedule.c
> +++ b/xen/common/schedule.c
> @@ -64,20 +64,10 @@ static void poll_timer_fn(void *data);
>  DEFINE_PER_CPU(struct schedule_data, schedule_data);
>  DEFINE_PER_CPU(struct scheduler *, scheduler);
>  
> -static const struct scheduler *schedulers[] = {
> -#ifdef CONFIG_SCHED_CREDIT
> -    &sched_credit_def,
> -#endif
> -#ifdef CONFIG_SCHED_CREDIT2
> -    &sched_credit2_def,
> -#endif
> -#ifdef CONFIG_SCHED_ARINC653
> -    &sched_arinc653_def,
> -#endif
> -#ifdef CONFIG_SCHED_RTDS
> -    &sched_rtds_def,
> -#endif
> -};
> +extern const struct scheduler *__schedulers_start[], *__schedulers_end[];
> +#define NUM_SCHEDULERS (((uintptr_t)__schedulers_end-(uintptr_t)__schedulers_start) \
> +                        / sizeof(struct scheduler *))
> +static const struct scheduler **schedulers = __schedulers_start;

You should be able to play some tricks with getting the linker to set a
size of a variable it creates, which would hopefully avoid some of this
complexity.

>  
>  static struct scheduler __read_mostly ops;
>  
> @@ -1468,7 +1458,7 @@ void __init scheduler_init(void)
>  
>      open_softirq(SCHEDULE_SOFTIRQ, schedule);
>  
> -    for ( i = 0; i < ARRAY_SIZE(schedulers); i++ )
> +    for ( i = 0; i < NUM_SCHEDULERS; i++)
>      {
>          if ( schedulers[i]->global_init && schedulers[i]->global_init() < 0 )
>              schedulers[i] = NULL;
> @@ -1479,7 +1469,7 @@ void __init scheduler_init(void)
>      if ( !ops.name )
>      {
>          printk("Could not find scheduler: %s\n", opt_sched);
> -        for ( i = 0; i < ARRAY_SIZE(schedulers); i++ )
> +        for ( i = 0; i < NUM_SCHEDULERS; i++ )
>              if ( schedulers[i] )
>              {
>                  ops = *schedulers[i];
> @@ -1599,7 +1589,7 @@ struct scheduler *scheduler_alloc(unsigned int sched_id, int *perr)
>      int i;
>      struct scheduler *sched;
>  
> -    for ( i = 0; i < ARRAY_SIZE(schedulers); i++ )
> +    for ( i = 0; i < NUM_SCHEDULERS; i++ )
>          if ( schedulers[i] && schedulers[i]->sched_id == sched_id )
>              goto found;
>      *perr = -ENOENT;
> diff --git a/xen/include/xen/sched-if.h b/xen/include/xen/sched-if.h
> index 9c6e0f5..66dc9c8 100644
> --- a/xen/include/xen/sched-if.h
> +++ b/xen/include/xen/sched-if.h
> @@ -165,11 +165,6 @@ struct scheduler {
>      void         (*tick_resume)     (const struct scheduler *, unsigned int);
>  };
>  
> -extern const struct scheduler sched_credit_def;
> -extern const struct scheduler sched_credit2_def;
> -extern const struct scheduler sched_arinc653_def;
> -extern const struct scheduler sched_rtds_def;
> -

With these changes, you can make the structures themselves static, which
would be a nice tidyup.

~Andrew

>  #define REGISTER_SCHEDULER(x) static const struct scheduler *x##_entry \
>    __used_section(".data.schedulers") = &x;
>