[libbsd] EPOCH(9): Fix epoch call and drain

[Gedare Bloom]

Does this add a constraint in libbsd that it only works with SMP for
schedulers that support thread pinning? Is that a problem at all? Last
I checked, not all the SMP schedulers have pinning. Actually, I think
only the EDF SMP scheduler supports pinning.

On Fri, Jun 11, 2021 at 12:46 AM Sebastian Huber
<sebastian.huber at embedded-brains.de> wrote:
>
> Since the epoch call callbacks may lock/unlock a mutex the callbacks must be
> called from within thread context with thread dispatching enabled.  Use thread
> pinning to ensure that the calling thread stays on the right processor.  Use
> the interrupt server to ensure the thread context for the epoch drain.
> ---
>  rtemsbsd/rtems/rtems-kernel-epoch.c | 39 ++++++++++++++++++++++++++---
>  1 file changed, 35 insertions(+), 4 deletions(-)
>
> diff --git a/rtemsbsd/rtems/rtems-kernel-epoch.c b/rtemsbsd/rtems/rtems-kernel-epoch.c
> index 0c070bd8..642b5854 100644
> --- a/rtemsbsd/rtems/rtems-kernel-epoch.c
> +++ b/rtemsbsd/rtems/rtems-kernel-epoch.c
> @@ -349,15 +349,29 @@ epoch_call(epoch_t epoch, epoch_context_t ctx,
>      void (*callback) (epoch_context_t))
>  {
>         Per_CPU_Control *cpu_self;
> -       struct epoch_record *er;
>         struct epoch_pcpu *epcpu;
> +       struct epoch_record *er;
> +#ifdef RTEMS_SMP
> +       ISR_Level level;
> +       Thread_Control *executing;
> +
> +       _ISR_Local_disable(level);
> +       cpu_self = _Per_CPU_Get();
> +       executing = _Per_CPU_Get_executing(cpu_self);
> +       _Thread_Pin(executing);
> +       _ISR_Local_enable(level);
> +#endif
>
> -       cpu_self = _Thread_Dispatch_disable();
>         epcpu = PER_CPU_DATA_GET(cpu_self, struct epoch_pcpu, epoch);
>         epcpu->cb_count += 1;
>         er = EPOCH_GET_RECORD(cpu_self, epoch);
>         ck_epoch_call(&er->er_record, ctx, callback);
> +
> +#ifdef RTEMS_SMP
> +       cpu_self = _Thread_Dispatch_disable();
> +       _Thread_Unpin(executing, cpu_self);
>         _Thread_Dispatch_enable(cpu_self);
> +#endif
>  }
>
>  #ifdef INVARIANTS
> @@ -411,7 +425,7 @@ epoch_call_drain_cb(void *arg)
>         struct epoch_record *er;
>
>         epoch = arg;
> -       cpu = _Per_CPU_Get();
> +       cpu = _Per_CPU_Get_snapshot();
>         er = EPOCH_GET_RECORD(cpu, epoch);
>         epoch_call(epoch, &er->er_drain_ctx, epoch_drain_cb);
>  }
> @@ -425,6 +439,7 @@ epoch_drain_callbacks(epoch_t epoch)
>         uint32_t cpu_max;
>         rtems_id id;
>         rtems_status_code sc;
> +       rtems_interrupt_server_request req[CPU_MAXIMUM_PROCESSORS];
>  #else
>         struct epoch_record *er;
>  #endif
> @@ -433,6 +448,7 @@ epoch_drain_callbacks(epoch_t epoch)
>         mtx_lock(&epoch->e_drain_mtx);
>
>  #ifdef RTEMS_SMP
> +       memset(&req, 0, sizeof(req));
>         cpu_max = rtems_scheduler_get_processor_maximum();
>
>         for (cpu_index = 0; cpu_index <= cpu_max; ++cpu_index) {
> @@ -445,8 +461,15 @@ epoch_drain_callbacks(epoch_t epoch)
>         for (cpu_index = 0; cpu_index <= cpu_max; ++cpu_index) {
>                 sc = rtems_scheduler_ident_by_processor(cpu_index, &id);
>                 if (sc == RTEMS_SUCCESSFUL) {
> -                       _SMP_Unicast_action(cpu_index, epoch_call_drain_cb,
> +                       sc = rtems_interrupt_server_request_initialize(
> +                           cpu_index, &req[cpu_index], epoch_call_drain_cb,
>                             epoch);
> +                       if (sc == RTEMS_SUCCESSFUL) {
> +                               rtems_interrupt_server_request_submit(
> +                                   &req[cpu_index]);
> +                       } else {
> +                               panic("no interrupt server for epoch drain");
> +                       }
>                 }
>         }
>  #else
> @@ -461,4 +484,12 @@ epoch_drain_callbacks(epoch_t epoch)
>
>         mtx_unlock(&epoch->e_drain_mtx);
>         sx_xunlock(&epoch->e_drain_sx);
> +
> +#ifdef RTEMS_SMP
> +       for (cpu_index = 0; cpu_index <= cpu_max; ++cpu_index) {
> +               if (req[cpu_index].action.handler != NULL) {
> +                       rtems_interrupt_server_request_destroy(&req[cpu_index]);
> +               }
> +       }
> +#endif
>  }
> --
> 2.26.2
>
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