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/rcutree.c b/kernel/rcutree.c
index a7c6bce..45dcc20 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -52,6 +52,9 @@
#include <linux/prefetch.h>
#include "rcutree.h"
+#include <trace/events/rcu.h>
+
+#include "rcu.h"
/* Data structures. */
@@ -1190,17 +1193,22 @@
{
unsigned long flags;
struct rcu_head *next, *list, **tail;
- int count;
+ int bl, count;
/* If no callbacks are ready, just return.*/
- if (!cpu_has_callbacks_ready_to_invoke(rdp))
+ if (!cpu_has_callbacks_ready_to_invoke(rdp)) {
+ trace_rcu_batch_start(0, 0);
+ trace_rcu_batch_end(0);
return;
+ }
/*
* Extract the list of ready callbacks, disabling to prevent
* races with call_rcu() from interrupt handlers.
*/
local_irq_save(flags);
+ bl = rdp->blimit;
+ trace_rcu_batch_start(rdp->qlen, bl);
list = rdp->nxtlist;
rdp->nxtlist = *rdp->nxttail[RCU_DONE_TAIL];
*rdp->nxttail[RCU_DONE_TAIL] = NULL;
@@ -1218,11 +1226,12 @@
debug_rcu_head_unqueue(list);
__rcu_reclaim(list);
list = next;
- if (++count >= rdp->blimit)
+ if (++count >= bl)
break;
}
local_irq_save(flags);
+ trace_rcu_batch_end(count);
/* Update count, and requeue any remaining callbacks. */
rdp->qlen -= count;