Add option to turn off preemption state tracing

Preemption state tracing is only useful when debugging preemption-
and IPI-related races. Since it creates a lot of clutter in the logs,
this patch turns it off unless explicitly requested.

3 files changed, 17 insertions, 1 deletions

diff --git a/include/litmus/preempt.h b/include/litmus/preempt.h
index 260c6fe17986..380b886d78ff 100644
--- a/include/litmus/preempt.h
+++ b/include/litmus/preempt.h
@@ -10,7 +10,7 @@
 
 extern DEFINE_PER_CPU_SHARED_ALIGNED(atomic_t, resched_state);
 
-#ifdef CONFIG_DEBUG_KERNEL
+#ifdef CONFIG_PREEMPT_STATE_TRACE
 const char* sched_state_name(int s);
 #define TRACE_STATE(fmt, args...) TRACE("SCHED_STATE " fmt, args)
 #else
diff --git a/litmus/Kconfig b/litmus/Kconfig
index d7fde6f97e14..94b48e199577 100644
--- a/litmus/Kconfig
+++ b/litmus/Kconfig
@@ -199,6 +199,20 @@ config SCHED_DEBUG_TRACE_CALLER
 
          If unsure, say No.
 
+config PREEMPT_STATE_TRACE
+       bool "Trace preemption state machine transitions"
+       depends on SCHED_DEBUG_TRACE
+       default n
+       help
+         With this option enabled, each CPU will log when it transitions
+         states in the preemption state machine. This state machine is
+         used to determine how to react to IPIs (avoid races with in-flight IPIs).
+
+         Warning: this creates a lot of information in the debug trace. Only
+         recommended when you are debugging preemption-related races.
+
+         If unsure, say No.
+
 endmenu
 
 endmenu
diff --git a/litmus/preempt.c b/litmus/preempt.c
index ebe2e3461895..5704d0bf4c0b 100644
--- a/litmus/preempt.c
+++ b/litmus/preempt.c
@@ -30,8 +30,10 @@ void sched_state_will_schedule(struct task_struct* tsk)
                 /* Litmus tasks should never be subject to a remote
                  * set_tsk_need_resched(). */
                 BUG_ON(is_realtime(tsk));
+#ifdef CONFIG_PREEMPT_STATE_TRACE
         TRACE_TASK(tsk, "set_tsk_need_resched() ret:%p\n",
                    __builtin_return_address(0));
+#endif
 }
 
 /* Called by the IPI handler after another CPU called smp_send_resched(). */