Integrate ft_irq_fired() with Linux

This patch hooks up Feather-Trace's ft_irq_fired() handler with
Linux's interrupt handling infrastructure.

IRQ tracing: ft_irq_fired() only if irq_enter() was skipped

On x86, the rescheduling IPI path already calls irq_enter(), which
calls ft_irq_fired(), so we don't have to do it again.

IRQ tracing: don't count softirqs

Only triggered by irq_exit(), which implies that we called
irq_enter(), which means that we already traced the current
hard IRQ.

3 files changed, 24 insertions, 0 deletions

diff --git a/include/linux/hardirq.h b/include/linux/hardirq.h
index c683996110b1..7eec96ace9c7 100644
--- a/include/linux/hardirq.h
+++ b/include/linux/hardirq.h
@@ -7,6 +7,7 @@
 #include <linux/vtime.h>
 #include <asm/hardirq.h>
 
+#include <litmus/trace_irq.h>
 
 extern void synchronize_irq(unsigned int irq);
 extern bool synchronize_hardirq(unsigned int irq);
@@ -37,6 +38,7 @@ extern void rcu_nmi_exit(void);
                 account_irq_enter_time(current);        \
                 preempt_count_add(HARDIRQ_OFFSET);      \
                 trace_hardirq_enter();                  \
+                ft_irq_fired();                         \
         } while (0)
 
 /*
@@ -68,6 +70,7 @@ extern void irq_exit(void);
                 preempt_count_add(NMI_OFFSET + HARDIRQ_OFFSET); \
                 rcu_nmi_enter();                                \
                 trace_hardirq_enter();                          \
+                ft_irq_fired();                                 \
         } while (0)
 
 #define nmi_exit()                                              \
diff --git a/include/litmus/trace_irq.h b/include/litmus/trace_irq.h
new file mode 100644
index 000000000000..0d0c042ba9c3
--- /dev/null
+++ b/include/litmus/trace_irq.h
@@ -0,0 +1,14 @@
+#ifndef _LITMUS_TRACE_IRQ_H_
+#define _LITMUS_TRACE_IRQ_H_
+
+#ifdef CONFIG_SCHED_OVERHEAD_TRACE
+
+void ft_irq_fired(void);
+
+#else
+
+#define ft_irq_fired() /* nothing to do */
+
+#endif
+
+#endif
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 154fd689fe02..6440fe53d1a8 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1806,7 +1806,14 @@ void scheduler_ipi(void)
         preempt_fold_need_resched();
 
         if (llist_empty(&this_rq()->wake_list) && !got_nohz_idle_kick())
+        {
+#ifndef CONFIG_ARCH_CALLS_IRQ_ENTER_ON_RESCHED_IPI
+                /* If we don't call irq_enter(), we need to triggger the IRQ
+                 * tracing manually. */
+                ft_irq_fired();
+#endif
                 return;
+        }
 
         /*
          * Not all reschedule IPI handlers call irq_enter/irq_exit, since