rcu: Add event-tracing for RCU callback invocation
There was recently some controversy about the overhead of invoking RCU
callbacks. Add TRACE_EVENT()s to obtain fine-grained timings for the
start and stop of a batch of callbacks and also for each callback invoked.
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
diff --git a/kernel/rcutiny.c b/kernel/rcutiny.c
index f544e34..19453ba 100644
--- a/kernel/rcutiny.c
+++ b/kernel/rcutiny.c
@@ -37,6 +37,25 @@
#include <linux/cpu.h>
#include <linux/prefetch.h>
+#ifdef CONFIG_RCU_TRACE
+
+#include <trace/events/rcu.h>
+
+#else /* #ifdef CONFIG_RCU_TRACE */
+
+/* No by-default tracing in TINY_RCU: Keep TINY_RCU tiny! */
+static void trace_rcu_invoke_kfree_callback(struct rcu_head *rhp,
+ unsigned long offset)
+{
+}
+static void trace_rcu_invoke_callback(struct rcu_head *head)
+{
+}
+
+#endif /* #else #ifdef CONFIG_RCU_TRACE */
+
+#include "rcu.h"
+
/* Controls for rcu_kthread() kthread, replacing RCU_SOFTIRQ used previously. */
static struct task_struct *rcu_kthread_task;
static DECLARE_WAIT_QUEUE_HEAD(rcu_kthread_wq);
@@ -161,11 +180,15 @@
RCU_TRACE(int cb_count = 0);
/* If no RCU callbacks ready to invoke, just return. */
- if (&rcp->rcucblist == rcp->donetail)
+ if (&rcp->rcucblist == rcp->donetail) {
+ RCU_TRACE(trace_rcu_batch_start(0, -1));
+ RCU_TRACE(trace_rcu_batch_end(0));
return;
+ }
/* Move the ready-to-invoke callbacks to a local list. */
local_irq_save(flags);
+ RCU_TRACE(trace_rcu_batch_start(0, -1));
list = rcp->rcucblist;
rcp->rcucblist = *rcp->donetail;
*rcp->donetail = NULL;
@@ -187,6 +210,7 @@
RCU_TRACE(cb_count++);
}
RCU_TRACE(rcu_trace_sub_qlen(rcp, cb_count));
+ RCU_TRACE(trace_rcu_batch_end(cb_count));
}
/*