srcu: Push srcu_advance_batches() fastpath into common case

This commit simplifies the SRCU state machine by pushing the
srcu_advance_batches() idle-SRCU fastpath into the common case.  This is
done by giving srcu_reschedule() a delay parameter, which is zero in
the call from srcu_advance_batches().

This commit is a step towards numbering callbacks in order to
efficiently handle per-CPU callback lists.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

1 files changed, 7 insertions, 20 deletions

diff --git a/kernel/rcu/srcu.c b/kernel/rcu/srcu.c
index 7e7ecaa50dc5..821ecda873f2 100644
--- a/kernel/rcu/srcu.c
+++ b/kernel/rcu/srcu.c
@@ -399,8 +399,7 @@ void call_srcu(struct srcu_struct *sp, struct rcu_head *head,
 }
 EXPORT_SYMBOL_GPL(call_srcu);
 
-static void srcu_advance_batches(struct srcu_struct *sp, int trycount);
-static void srcu_reschedule(struct srcu_struct *sp);
+static void srcu_reschedule(struct srcu_struct *sp, unsigned long delay);
 
 /*
  * Helper function for synchronize_srcu() and synchronize_srcu_expedited().
@@ -409,7 +408,6 @@ static void __synchronize_srcu(struct srcu_struct *sp, int trycount)
 {
         struct rcu_synchronize rcu;
         struct rcu_head *head = &rcu.head;
-        bool done = false;
 
         RCU_LOCKDEP_WARN(lock_is_held(&sp->dep_map) ||
                          lock_is_held(&rcu_bh_lock_map) ||
@@ -431,25 +429,15 @@ static void __synchronize_srcu(struct srcu_struct *sp, int trycount)
                 sp->running = true;
                 rcu_batch_queue(&sp->batch_check0, head);
                 spin_unlock_irq(&sp->queue_lock);
-
-                srcu_advance_batches(sp, trycount);
-                if (!rcu_batch_empty(&sp->batch_done)) {
-                        BUG_ON(sp->batch_done.head != head);
-                        rcu_batch_dequeue(&sp->batch_done);
-                        done = true;
-                }
                 /* give the processing owner to work_struct */
-                srcu_reschedule(sp);
+                srcu_reschedule(sp, 0);
         } else {
                 rcu_batch_queue(&sp->batch_queue, head);
                 spin_unlock_irq(&sp->queue_lock);
         }
 
-        if (!done) {
-                wait_for_completion(&rcu.completion);
-                smp_mb(); /* Caller's later accesses after GP. */
-        }
-
+        wait_for_completion(&rcu.completion);
+        smp_mb(); /* Caller's later accesses after GP. */
 }
 
 /**
@@ -639,7 +627,7 @@ static void srcu_invoke_callbacks(struct srcu_struct *sp)
  * Finished one round of SRCU grace period.  Start another if there are
  * more SRCU callbacks queued, otherwise put SRCU into not-running state.
  */
-static void srcu_reschedule(struct srcu_struct *sp)
+static void srcu_reschedule(struct srcu_struct *sp, unsigned long delay)
 {
         bool pending = true;
 
@@ -653,8 +641,7 @@ static void srcu_reschedule(struct srcu_struct *sp)
         }
 
         if (pending)
-                queue_delayed_work(system_power_efficient_wq,
-                                   &sp->work, SRCU_INTERVAL);
+                queue_delayed_work(system_power_efficient_wq, &sp->work, delay);
 }
 
 /*
@@ -669,6 +656,6 @@ void process_srcu(struct work_struct *work)
         srcu_collect_new(sp);
         srcu_advance_batches(sp, 1);
         srcu_invoke_callbacks(sp);
-        srcu_reschedule(sp);
+        srcu_reschedule(sp, SRCU_INTERVAL);
 }
 EXPORT_SYMBOL_GPL(process_srcu);