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

[Jonathan Creekmore <jonathan.creekmore@xxxxxxxxx>]

Andrew Cooper writes:

> 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@xxxxxxxxxxxxx>
>> CC: Dario Faggioli <dario.faggioli@xxxxxxxxxx>
>> Signed-off-by: Jonathan Creekmore <jonathan.creekmore@xxxxxxxxx>
>> ---
>>  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.

Yeah, that looks fairly straightforward. I can do that in a v2.

>>
>>  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.
>

I like that as well and will handle that in the v2.

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