rcu: Update RCU_FAST_NO_HZ tracing for lazy callbacks

In the current code, a short dyntick-idle interval (where there is
at least one non-lazy callback on the CPU) and a long dyntick-idle
interval (where there are only lazy callbacks on the CPU) are traced
identically, which can be less than helpful.  This commit therefore
emits different event traces in these two cases.

Signed-off-by: Paul E. McKenney <[email protected]>
Signed-off-by: Paul E. McKenney <[email protected]>
Tested-by: Heiko Carstens <[email protected]>
Tested-by: Pascal Chapperon <[email protected]>

diff --git a/include/trace/events/rcu.h b/include/trace/events/rcu.h
index 1480900c511ce134443e7bf2f41d8e5ba0f97117..d274734b2aa42fee56d7ce7ab2b7898d39521e7e 100644 (file)
--- a/include/trace/events/rcu.h
+++ b/include/trace/events/rcu.h
@@ -289,6 +289,7 @@ TRACE_EVENT(rcu_dyntick,
  *     "In holdoff": Nothing to do, holding off after unsuccessful attempt.
  *     "Begin holdoff": Attempt failed, don't retry until next jiffy.
  *     "Dyntick with callbacks": Entering dyntick-idle despite callbacks.
+ *     "Dyntick with lazy callbacks": Entering dyntick-idle w/lazy callbacks.
  *     "More callbacks": Still more callbacks, try again to clear them out.
  *     "Callbacks drained": All callbacks processed, off to dyntick idle!
  *     "Timer": Timer fired to cause CPU to continue processing callbacks.

diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index 2411000d98690aacd76d20acc039964402e83388..5449f02c48203441608d044372c3ab821b30dfff 100644 (file)
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -2165,15 +2165,17 @@ static void rcu_prepare_for_idle(int cpu)
                   !rcu_pending(cpu) &&
                   !local_softirq_pending()) {
                /* Can we go dyntick-idle despite still having callbacks? */
-               trace_rcu_prep_idle("Dyntick with callbacks");
                per_cpu(rcu_dyntick_drain, cpu) = 0;
                per_cpu(rcu_dyntick_holdoff, cpu) = jiffies;
-               if (rcu_cpu_has_nonlazy_callbacks(cpu))
+               if (rcu_cpu_has_nonlazy_callbacks(cpu)) {
+                       trace_rcu_prep_idle("Dyntick with callbacks");
                        per_cpu(rcu_idle_gp_timer_expires, cpu) =
                                           jiffies + RCU_IDLE_GP_DELAY;
-               else
+               } else {
                        per_cpu(rcu_idle_gp_timer_expires, cpu) =
                                           jiffies + RCU_IDLE_LAZY_GP_DELAY;
+                       trace_rcu_prep_idle("Dyntick with lazy callbacks");
+               }
                tp = &per_cpu(rcu_idle_gp_timer, cpu);
                mod_timer_pinned(tp, per_cpu(rcu_idle_gp_timer_expires, cpu));
                per_cpu(rcu_nonlazy_posted_snap, cpu) =