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, 4 insertions, 7 deletions

diff --git a/litmus/sched_pfair.c b/litmus/sched_pfair.c
index ea77d3295290..c7d5cf7aa2b3 100644
--- a/litmus/sched_pfair.c
+++ b/litmus/sched_pfair.c
@@ -16,6 +16,7 @@
 
 #include <litmus/litmus.h>
 #include <litmus/jobs.h>
+#include <litmus/preempt.h>
 #include <litmus/rt_domain.h>
 #include <litmus/sched_plugin.h>
 #include <litmus/sched_trace.h>
@@ -241,11 +242,7 @@ static void check_preempt(struct task_struct* t)
                 PTRACE_TASK(t, "linked_on:%d, scheduled_on:%d\n",
                            tsk_rt(t)->linked_on, tsk_rt(t)->scheduled_on);
                 /* preempt */
-                if (cpu == smp_processor_id())
-                        set_tsk_need_resched(current);
-                else {
-                        smp_send_reschedule(cpu);
-                }
+                litmus_reschedule(cpu);
         }
 }
 
@@ -545,7 +542,7 @@ static void pfair_tick(struct task_struct* t)
 
         if (state->local != current
             && (is_realtime(current) || is_present(state->local)))
-                set_tsk_need_resched(current);
+                litmus_reschedule_local();
 }
 
 static int safe_to_schedule(struct task_struct* t, int cpu)
@@ -577,7 +574,7 @@ static struct task_struct* pfair_schedule(struct task_struct * prev)
                 if (next)
                         tsk_rt(next)->scheduled_on = state->cpu;
         }
-
+        sched_state_task_picked();
         raw_spin_unlock(&pfair_lock);
 
         if (next)