rcu: Introduce proper blocking to no-CBs kthreads GP waits

Currently, the no-CBs kthreads do repeated timed waits for grace periods
to elapse.  This is crude and energy inefficient, so this commit allows
no-CBs kthreads to specify exactly which grace period they are waiting
for and also allows them to block for the entire duration until the
desired grace period completes.

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

1 files changed, 5 insertions, 1 deletions

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 6ad0716e65dc..433f426c848f 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -310,7 +310,7 @@ cpu_needs_another_gp(struct rcu_state *rsp, struct rcu_data *rdp)
 
         if (rcu_gp_in_progress(rsp))
                 return 0;  /* No, a grace period is already in progress. */
-        if (rcu_nocb_needs_gp(rdp))
+        if (rcu_nocb_needs_gp(rsp))
                 return 1;  /* Yes, a no-CBs CPU needs one. */
         if (!rdp->nxttail[RCU_NEXT_TAIL])
                 return 0;  /* No, this is a no-CBs (or offline) CPU. */
@@ -1364,6 +1364,7 @@ int rcu_gp_fqs(struct rcu_state *rsp, int fqs_state_in)
 static void rcu_gp_cleanup(struct rcu_state *rsp)
 {
         unsigned long gp_duration;
+        int nocb = 0;
         struct rcu_data *rdp;
         struct rcu_node *rnp = rcu_get_root(rsp);
 
@@ -1394,11 +1395,13 @@ static void rcu_gp_cleanup(struct rcu_state *rsp)
         rcu_for_each_node_breadth_first(rsp, rnp) {
                 raw_spin_lock_irq(&rnp->lock);
                 rnp->completed = rsp->gpnum;
+                nocb += rcu_nocb_gp_cleanup(rsp, rnp);
                 raw_spin_unlock_irq(&rnp->lock);
                 cond_resched();
         }
         rnp = rcu_get_root(rsp);
         raw_spin_lock_irq(&rnp->lock);
+        rcu_nocb_gp_set(rnp, nocb);
 
         rsp->completed = rsp->gpnum; /* Declare grace period done. */
         trace_rcu_grace_period(rsp->name, rsp->completed, "end");
@@ -3084,6 +3087,7 @@ static void __init rcu_init_one(struct rcu_state *rsp,
                         }
                         rnp->level = i;
                         INIT_LIST_HEAD(&rnp->blkd_tasks);
+                        rcu_init_one_nocb(rnp);
                 }
         }