rcu: Add __rcu_pending tracing to hierarchical RCU

Add tracing to __rcu_pending() to provide information on why RCU
processing was kicked off.  This is helpful for debugging hierarchical
RCU, and might also be helpful in learning how hierarchical RCU operates.

Located-by: Anton Blanchard <anton@au1.ibm.com>
Tested-by: Anton Blanchard <anton@au1.ibm.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: anton@samba.org
Cc: akpm@linux-foundation.org
Cc: dipankar@in.ibm.com
Cc: manfred@colorfullife.com
Cc: cl@linux-foundation.org
Cc: josht@linux.vnet.ibm.com
Cc: schamp@sgi.com
Cc: niv@us.ibm.com
Cc: dvhltc@us.ibm.com
Cc: ego@in.ibm.com
Cc: laijs@cn.fujitsu.com
Cc: rostedt@goodmis.org
Cc: peterz@infradead.org
Cc: penberg@cs.helsinki.fi
Cc: andi@firstfloor.org
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
LKML-Reference: <1239683479943-git-send-email->
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 8 insertions, 1 deletions

diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
index 58b2aa5312b9..5a5153806c42 100644
--- a/include/linux/rcutree.h
+++ b/include/linux/rcutree.h
@@ -161,8 +161,15 @@ struct rcu_data {
         unsigned long offline_fqs;      /* Kicked due to being offline. */
         unsigned long resched_ipi;      /* Sent a resched IPI. */
 
-        /* 5) For future __rcu_pending statistics. */
+        /* 5) __rcu_pending() statistics. */
         long n_rcu_pending;             /* rcu_pending() calls since boot. */
+        long n_rp_qs_pending;
+        long n_rp_cb_ready;
+        long n_rp_cpu_needs_gp;
+        long n_rp_gp_completed;
+        long n_rp_gp_started;
+        long n_rp_need_fqs;
+        long n_rp_need_nothing;
 
         int cpu;
 };