[PATCH 3/3] score: Task get/set affinity

[Joel Sherrill]

On 4/10/2014 3:42 AM, Sebastian Huber wrote:
> On 2014-04-10 04:27, Chris Johns wrote:
>>>> The short circuit logic for non-smp should be in the api level code
>>>> and the
>>>> score should have NO code for affinity.
>>> Since the affinity support is used by the Classic and POSIX API it must
>>> stay in the score.
>> Conditionally removed on uniprocessor builds ?
>>
>>>> Otherwise you impact the minimum profile and this is 100% unacceptable.
>>> There is no overhead in the non-SMP configurations if you don't use the
>>> task set/get affinity functions.  The scheduler get/set affinity
>>> operations are only available in SMP configurations.
>>>
>> Could you please elaborate ? If I do not use the functions the score includes
>> no extra code related to this API, ie the scope is limited to the API layer ?
> Lets look at rtems_task_get_affinity() for example.  This function makes sense 
> on a uni-processor system since this can be viewed as an SMP system with only 
> one processor.  The implementation is like this:
>
> rtems_status_code rtems_task_get_affinity(
>    rtems_id             id,
>    size_t               cpusetsize,
>    cpu_set_t           *cpuset
> )
> {
>    Thread_Control        *the_thread;
>    Objects_Locations      location;
>    bool                   ok;
>
>    if ( !cpuset )
>      return RTEMS_INVALID_ADDRESS;
>
>    the_thread = _Thread_Get( id, &location );
>
>    switch ( location ) {
>
>      case OBJECTS_LOCAL:
>        ok = _Scheduler_Get_affinity(
>          _Scheduler_Get( the_thread ),
>          the_thread,
>          cpusetsize,
>          cpuset
>        );
>        _Objects_Put( &the_thread->Object );
>        return ok ? RTEMS_SUCCESSFUL : RTEMS_INVALID_NUMBER;
>
> #if defined(RTEMS_MULTIPROCESSING)
>      case OBJECTS_REMOTE:
> #endif
>
>      case OBJECTS_ERROR:
>        break;
>    }
>
>    return RTEMS_INVALID_ID;
> }
>
> This leads to _Scheduler_Get_affinity():
>
> bool _Scheduler_Get_affinity(
>    const Scheduler_Control *scheduler,
>    Thread_Control          *the_thread,
>    size_t                   cpusetsize,
>    cpu_set_t               *cpuset
> )
> {
>    bool ok;
>
>    if ( _CPU_set_Is_large_enough( cpusetsize ) ) {
> #if defined(RTEMS_SMP)
>      ok = ( *scheduler->Operations.get_affinity )(
>        scheduler,
>        the_thread,
>        cpusetsize,
>        cpuset
>      );
> #else
>      ok = _Scheduler_default_Get_affinity_body(
>        scheduler,
>        the_thread,
>        cpusetsize,
>        cpuset
>      );
> #endif
>    } else {
>      ok = false;
>    }
>
>    return ok;
> }
>
> On non-SMP this leads to _Scheduler_default_Get_affinity_body().  Please note 
> that we have no get/set affinity operation!

I am sorry. I misread this code in the patch. It is clearly only going
to result in code
being included in an application if the app makes the affinity calls. 
For some reason,
that wasn't clear to me in a diff format.
> RTEMS_INLINE_ROUTINE bool _Scheduler_default_Get_affinity_body(
>    const Scheduler_Control *scheduler,
>    Thread_Control          *the_thread,
>    size_t                   cpusetsize,
>    cpu_set_t               *cpuset
> )
> {
>    uint32_t cpu_count = _SMP_Get_processor_count();
>    uint32_t cpu_index;
>
>    (void) scheduler;
>    (void) the_thread;
>
>    CPU_ZERO_S( cpusetsize, cpuset );
>
>    for ( cpu_index = 0 ; cpu_index < cpu_count ; ++cpu_index ) {
>      CPU_SET_S( (int) cpu_index, cpusetsize, cpuset );
>    }
>
>    return true;
> }
>
> On non-SMP _SMP_Get_processor_count() is a compile-time constant of one.
>
> So if you use rtems_task_get_affinity() on non-SMP you have of course the 
> overhead for this function to return a cpuset with all bits except bit 0 set to 
> zero.  You have no overhead in the rest of the system, e.g. not set/get 
> affinity operations in the scheduler, global variables, structure variables, etc.
>

-- 
Joel Sherrill, Ph.D.             Director of Research & Development
joel.sherrill at OARcorp.com        On-Line Applications Research
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