Implement proper remote preemption support

To date, Litmus has just hooked into the smp_send_reschedule() IPI
handler and marked tasks as having to reschedule to implement remote
preemptions. This was never particularly clean, but so far we got away
with it. However, changes in the underlying Linux, and peculartities
of the ARM code (interrupts enabled before context switch) break this
naive approach. This patch introduces new state-machine based remote
preemption support. By examining the local state before calling
set_tsk_need_resched(), we avoid confusing the underlying Linux
scheduler. Further, this patch avoids sending unncessary IPIs.

1 files changed, 3 insertions, 1 deletions

diff --git a/litmus/sched_psn_edf.c b/litmus/sched_psn_edf.c
index aa567f2b91b9..b89823d5c026 100644
--- a/litmus/sched_psn_edf.c
+++ b/litmus/sched_psn_edf.c
@@ -16,6 +16,7 @@
 
 #include <litmus/litmus.h>
 #include <litmus/jobs.h>
+#include <litmus/preempt.h>
 #include <litmus/sched_plugin.h>
 #include <litmus/edf_common.h>
 #include <litmus/sched_trace.h>
@@ -108,7 +109,7 @@ static void psnedf_tick(struct task_struct *t)
 
         if (is_realtime(t) && budget_enforced(t) && budget_exhausted(t)) {
                 if (!is_np(t)) {
-                        set_tsk_need_resched(t);
+                        litmus_reschedule_local();
                         TRACE("psnedf_scheduler_tick: "
                               "%d is preemptable "
                               " => FORCE_RESCHED\n", t->pid);
@@ -204,6 +205,7 @@ static struct task_struct* psnedf_schedule(struct task_struct * prev)
         }
 
         pedf->scheduled = next;
+        sched_state_task_picked();
         raw_spin_unlock(&pedf->slock);
 
         return next;