rcu: Add tracing for _rcu_barrier()

This commit adds event tracing for _rcu_barrier() execution.  This
is defined only if RCU_TRACE=y.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>

1 files changed, 28 insertions, 1 deletions

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 6bb5d562253f..dda43d826504 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -2260,6 +2260,17 @@ static int rcu_cpu_has_callbacks(int cpu)
 }
 
 /*
+ * Helper function for _rcu_barrier() tracing.  If tracing is disabled,
+ * the compiler is expected to optimize this away.
+ */
+static void _rcu_barrier_trace(struct rcu_state *rsp, char *s,
+                               int cpu, unsigned long done)
+{
+        trace_rcu_barrier(rsp->name, s, cpu,
+                          atomic_read(&rsp->barrier_cpu_count), done);
+}
+
+/*
  * RCU callback function for _rcu_barrier().  If we are last, wake
  * up the task executing _rcu_barrier().
  */
@@ -2268,8 +2279,12 @@ static void rcu_barrier_callback(struct rcu_head *rhp)
         struct rcu_data *rdp = container_of(rhp, struct rcu_data, barrier_head);
         struct rcu_state *rsp = rdp->rsp;
 
-        if (atomic_dec_and_test(&rsp->barrier_cpu_count))
+        if (atomic_dec_and_test(&rsp->barrier_cpu_count)) {
+                _rcu_barrier_trace(rsp, "LastCB", -1, rsp->n_barrier_done);
                 complete(&rsp->barrier_completion);
+        } else {
+                _rcu_barrier_trace(rsp, "CB", -1, rsp->n_barrier_done);
+        }
 }
 
 /*
@@ -2280,6 +2295,7 @@ static void rcu_barrier_func(void *type)
         struct rcu_state *rsp = type;
         struct rcu_data *rdp = __this_cpu_ptr(rsp->rda);
 
+        _rcu_barrier_trace(rsp, "IRQ", -1, rsp->n_barrier_done);
         atomic_inc(&rsp->barrier_cpu_count);
         rsp->call(&rdp->barrier_head, rcu_barrier_callback);
 }
@@ -2298,6 +2314,7 @@ static void _rcu_barrier(struct rcu_state *rsp)
         unsigned long snap_done;
 
         init_rcu_head_on_stack(&rd.barrier_head);
+        _rcu_barrier_trace(rsp, "Begin", -1, snap);
 
         /* Take mutex to serialize concurrent rcu_barrier() requests. */
         mutex_lock(&rsp->barrier_mutex);
@@ -2315,7 +2332,9 @@ static void _rcu_barrier(struct rcu_state *rsp)
          * value up to the next even number and adds two before comparing.
          */
         snap_done = ACCESS_ONCE(rsp->n_barrier_done);
+        _rcu_barrier_trace(rsp, "Check", -1, snap_done);
         if (ULONG_CMP_GE(snap_done, ((snap + 1) & ~0x1) + 2)) {
+                _rcu_barrier_trace(rsp, "EarlyExit", -1, snap_done);
                 smp_mb(); /* caller's subsequent code after above check. */
                 mutex_unlock(&rsp->barrier_mutex);
                 return;
@@ -2328,6 +2347,7 @@ static void _rcu_barrier(struct rcu_state *rsp)
          */
         ACCESS_ONCE(rsp->n_barrier_done)++;
         WARN_ON_ONCE((rsp->n_barrier_done & 0x1) != 1);
+        _rcu_barrier_trace(rsp, "Inc1", -1, rsp->n_barrier_done);
         smp_mb(); /* Order ->n_barrier_done increment with below mechanism. */
 
         /*
@@ -2364,13 +2384,19 @@ static void _rcu_barrier(struct rcu_state *rsp)
                 preempt_disable();
                 rdp = per_cpu_ptr(rsp->rda, cpu);
                 if (cpu_is_offline(cpu)) {
+                        _rcu_barrier_trace(rsp, "Offline", cpu,
+                                           rsp->n_barrier_done);
                         preempt_enable();
                         while (cpu_is_offline(cpu) && ACCESS_ONCE(rdp->qlen))
                                 schedule_timeout_interruptible(1);
                 } else if (ACCESS_ONCE(rdp->qlen)) {
+                        _rcu_barrier_trace(rsp, "OnlineQ", cpu,
+                                           rsp->n_barrier_done);
                         smp_call_function_single(cpu, rcu_barrier_func, rsp, 1);
                         preempt_enable();
                 } else {
+                        _rcu_barrier_trace(rsp, "OnlineNQ", cpu,
+                                           rsp->n_barrier_done);
                         preempt_enable();
                 }
         }
@@ -2403,6 +2429,7 @@ static void _rcu_barrier(struct rcu_state *rsp)
         smp_mb(); /* Keep increment after above mechanism. */
         ACCESS_ONCE(rsp->n_barrier_done)++;
         WARN_ON_ONCE((rsp->n_barrier_done & 0x1) != 0);
+        _rcu_barrier_trace(rsp, "Inc2", -1, rsp->n_barrier_done);
         smp_mb(); /* Keep increment before caller's subsequent code. */
 
         /* Wait for all rcu_barrier_callback() callbacks to be invoked. */