rcu: Refactor rcu_barrier() empty-list handling

This commit saves a few lines by checking first for an empty callback
list.  If the callback list is empty, then that CPU is taken care of,
regardless of its online or nocb state.  Also simplify tracing accordingly
and fold a few lines together.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

diff --git a/include/trace/events/rcu.h b/include/trace/events/rcu.h
index 670e41783edd8a27e54a80a1fc8f87a5cb85e3a9..90b2fb0292cb1525d7ecd1f82f10b163804f7ee0 100644 (file)
--- a/include/trace/events/rcu.h
+++ b/include/trace/events/rcu.h
@@ -794,16 +794,15 @@ TRACE_EVENT_RCU(rcu_torture_read,
  * Tracepoint for rcu_barrier() execution.  The string "s" describes
  * the rcu_barrier phase:
  *     "Begin": rcu_barrier() started.
+ *     "CB": An rcu_barrier_callback() invoked a callback, not the last.
  *     "EarlyExit": rcu_barrier() piggybacked, thus early exit.
  *     "Inc1": rcu_barrier() piggyback check counter incremented.
- *     "OfflineNoCBQ": rcu_barrier() found offline no-CBs CPU with callbacks.
- *     "OnlineQ": rcu_barrier() found online CPU with callbacks.
- *     "OnlineNQ": rcu_barrier() found online CPU, no callbacks.
+ *     "Inc2": rcu_barrier() piggyback check counter incremented.
  *     "IRQ": An rcu_barrier_callback() callback posted on remote CPU.
  *     "IRQNQ": An rcu_barrier_callback() callback found no callbacks.
- *     "CB": An rcu_barrier_callback() invoked a callback, not the last.
  *     "LastCB": An rcu_barrier_callback() invoked the last callback.
- *     "Inc2": rcu_barrier() piggyback check counter incremented.
+ *     "NQ": rcu_barrier() found a CPU with no callbacks.
+ *     "OnlineQ": rcu_barrier() found online CPU with callbacks.
  * The "cpu" argument is the CPU or -1 if meaningless, the "cnt" argument
  * is the count of remaining callbacks, and "done" is the piggybacking count.
  */

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 73a4c9d07b8651f04bb08f6a1ee308ecb4fcf4ec..57a7a0065750b68dea57d4aed7b0f4df2ef295c3 100644 (file)
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -4030,8 +4030,7 @@ void rcu_barrier(void)
 
        /* Did someone else do our work for us? */
        if (rcu_seq_done(&rcu_state.barrier_sequence, s)) {
-               rcu_barrier_trace(TPS("EarlyExit"), -1,
-                                 rcu_state.barrier_sequence);
+               rcu_barrier_trace(TPS("EarlyExit"), -1, rcu_state.barrier_sequence);
                smp_mb(); /* caller's subsequent code after above check. */
                mutex_unlock(&rcu_state.barrier_mutex);
                return;
@@ -4059,26 +4058,18 @@ void rcu_barrier(void)
         */
        for_each_possible_cpu(cpu) {
                rdp = per_cpu_ptr(&rcu_data, cpu);
-               if (cpu_is_offline(cpu) &&
-                   !rcu_rdp_is_offloaded(rdp))
+               if (!rcu_segcblist_n_cbs(&rdp->cblist)) {
+                       rcu_barrier_trace(TPS("NQ"), cpu, rcu_state.barrier_sequence);
                        continue;
-               if (rcu_segcblist_n_cbs(&rdp->cblist) && cpu_online(cpu)) {
-                       rcu_barrier_trace(TPS("OnlineQ"), cpu,
-                                         rcu_state.barrier_sequence);
+               }
+               if (cpu_online(cpu)) {
+                       rcu_barrier_trace(TPS("OnlineQ"), cpu, rcu_state.barrier_sequence);
                        smp_call_function_single(cpu, rcu_barrier_func, (void *)cpu, 1);
-               } else if (rcu_segcblist_n_cbs(&rdp->cblist) &&
-                          cpu_is_offline(cpu)) {
-                       rcu_barrier_trace(TPS("OfflineNoCBQ"), cpu,
-                                         rcu_state.barrier_sequence);
+               } else {
+                       rcu_barrier_trace(TPS("OfflineNoCBQ"), cpu, rcu_state.barrier_sequence);
                        local_irq_disable();
                        rcu_barrier_func((void *)cpu);
                        local_irq_enable();
-               } else if (cpu_is_offline(cpu)) {
-                       rcu_barrier_trace(TPS("OfflineNoCBNoQ"), cpu,
-                                         rcu_state.barrier_sequence);
-               } else {
-                       rcu_barrier_trace(TPS("OnlineNQ"), cpu,
-                                         rcu_state.barrier_sequence);
                }
        }
        cpus_read_unlock();