[PATCH] rcu/dyntick-idle: Add better tracing

["Joel Fernandes (Google)" <joel@xxxxxxxxxxxxxxxxx>]

The dyntick-idle traces are a bit confusing. This patch makes it simpler
and adds some missing cases such as EQS-enter because user vs idle mode.

Following are the changes:
(1) Add a new context field to trace_rcu_dyntick tracepoint. This
    context field can be "USER", "IDLE" or "IRQ".

(2) Remove the "++=" and "--=" strings and replace them with
   "StillNonIdle". This is much easier on the eyes, and the -- and ++
   are easily apparent in the dynticks_nesting counters we are printing
   anyway.

This patch is based on the previous patches to simplify rcu_dyntick
counters [1] and with these traces, I have verified the counters are
working properly.

[1]
Link: https://lore.kernel.org/patchwork/patch/1120021/
Link: https://lore.kernel.org/patchwork/patch/1120022/

Signed-off-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
---
 include/trace/events/rcu.h | 13 ++++++++-----
 kernel/rcu/tree.c          | 17 +++++++++++------
 2 files changed, 19 insertions(+), 11 deletions(-)

diff --git a/include/trace/events/rcu.h b/include/trace/events/rcu.h
index 66122602bd08..474c1f7e7104 100644
--- a/include/trace/events/rcu.h
+++ b/include/trace/events/rcu.h
@@ -449,12 +449,14 @@ TRACE_EVENT_RCU(rcu_fqs,
  */
 TRACE_EVENT_RCU(rcu_dyntick,
 
-	TP_PROTO(const char *polarity, long oldnesting, long newnesting, atomic_t dynticks),
+	TP_PROTO(const char *polarity, const char *context, long oldnesting,
+		 long newnesting, atomic_t dynticks),
 
-	TP_ARGS(polarity, oldnesting, newnesting, dynticks),
+	TP_ARGS(polarity, context, oldnesting, newnesting, dynticks),
 
 	TP_STRUCT__entry(
 		__field(const char *, polarity)
+		__field(const char *, context)
 		__field(long, oldnesting)
 		__field(long, newnesting)
 		__field(int, dynticks)
@@ -462,14 +464,15 @@ TRACE_EVENT_RCU(rcu_dyntick,
 
 	TP_fast_assign(
 		__entry->polarity = polarity;
+		__entry->context = context;
 		__entry->oldnesting = oldnesting;
 		__entry->newnesting = newnesting;
 		__entry->dynticks = atomic_read(&dynticks);
 	),
 
-	TP_printk("%s %lx %lx %#3x", __entry->polarity,
-		  __entry->oldnesting, __entry->newnesting,
-		  __entry->dynticks & 0xfff)
+	TP_printk("%s %s %lx %lx %#3x", __entry->polarity,
+		__entry->context, __entry->oldnesting, __entry->newnesting,
+		__entry->dynticks & 0xfff)
 );
 
 /*
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 1465a3e406f8..1a65919ec800 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -570,7 +570,8 @@ static void rcu_eqs_enter(bool user)
 	}
 
 	lockdep_assert_irqs_disabled();
-	trace_rcu_dyntick(TPS("Start"), rdp->dynticks_nesting, 0, rdp->dynticks);
+	trace_rcu_dyntick(TPS("Start"), (user ? TPS("USER") : TPS("IDLE")),
+			  rdp->dynticks_nesting, 0, rdp->dynticks);
 	WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !user && !is_idle_task(current));
 	rdp = this_cpu_ptr(&rcu_data);
 	do_nocb_deferred_wakeup(rdp);
@@ -642,15 +643,17 @@ static __always_inline void rcu_nmi_exit_common(bool irq)
 	 * leave it in non-RCU-idle state.
 	 */
 	if (rdp->dynticks_nesting != 1) {
-		trace_rcu_dyntick(TPS("--="), rdp->dynticks_nesting,
-				  rdp->dynticks_nesting - 2, rdp->dynticks);
+		trace_rcu_dyntick(TPS("StillNonIdle"), TPS("IRQ"),
+				  rdp->dynticks_nesting, rdp->dynticks_nesting - 2,
+				  rdp->dynticks);
 		WRITE_ONCE(rdp->dynticks_nesting, /* No store tearing. */
 			   rdp->dynticks_nesting - 2);
 		return;
 	}
 
 	/* This NMI interrupted an RCU-idle CPU, restore RCU-idleness. */
-	trace_rcu_dyntick(TPS("Startirq"), rdp->dynticks_nesting, 0, rdp->dynticks);
+	trace_rcu_dyntick(TPS("Start"), TPS("IRQ"), rdp->dynticks_nesting, 0,
+			  rdp->dynticks);
 	WRITE_ONCE(rdp->dynticks_nesting, 0); /* Avoid store tearing. */
 
 	if (irq)
@@ -733,7 +736,8 @@ static void rcu_eqs_exit(bool user)
 	rcu_dynticks_task_exit();
 	rcu_dynticks_eqs_exit();
 	rcu_cleanup_after_idle();
-	trace_rcu_dyntick(TPS("End"), rdp->dynticks_nesting, 1, rdp->dynticks);
+	trace_rcu_dyntick(TPS("End"), (user ? TPS("USER") : TPS("IDLE")),
+			  rdp->dynticks_nesting, 1, rdp->dynticks);
 	WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !user && !is_idle_task(current));
 	WRITE_ONCE(rdp->dynticks_nesting, 1);
 
@@ -825,7 +829,8 @@ static __always_inline void rcu_nmi_enter_common(bool irq)
 		tick_dep_set_cpu(rdp->cpu, TICK_DEP_BIT_RCU);
 	}
 
-	trace_rcu_dyntick(incby == 1 ? TPS("Endirq") : TPS("++="),
+	trace_rcu_dyntick(incby == 1 ? TPS("End") : TPS("StillNonIdle"),
+			  TPS("IRQ"),
 			  rdp->dynticks_nesting,
 			  rdp->dynticks_nesting + incby, rdp->dynticks);
 
-- 
2.23.0.187.g17f5b7556c-goog