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Subject[PATCH tip/core/rcu 12/22] rcu: Add tracing for _rcu_barrier()
Date
From: "Paul E. McKenney" <paul.mckenney@linaro.org>

This commit adds event tracing for _rcu_barrier() execution. This
is defined only if RCU_TRACE=y.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
---
include/trace/events/rcu.h | 45 ++++++++++++++++++++++++++++++++++++++++++++
kernel/rcutree.c | 29 +++++++++++++++++++++++++++-
2 files changed, 73 insertions(+), 1 deletions(-)
diff --git a/include/trace/events/rcu.h b/include/trace/events/rcu.h
index 1480900..cd63f79 100644
--- a/include/trace/events/rcu.h
+++ b/include/trace/events/rcu.h
@@ -540,6 +540,50 @@ TRACE_EVENT(rcu_torture_read,
__entry->rcutorturename, __entry->rhp)
);

+/*
+ * Tracepoint for _rcu_barrier() execution. The string "s" describes
+ * the _rcu_barrier phase:
+ * "Begin": rcu_barrier_callback() started.
+ * "Check": rcu_barrier_callback() checking for piggybacking.
+ * "EarlyExit": rcu_barrier_callback() piggybacked, thus early exit.
+ * "Inc1": rcu_barrier_callback() piggyback check counter incremented.
+ * "Offline": rcu_barrier_callback() found offline CPU
+ * "OnlineQ": rcu_barrier_callback() found online CPU with callbacks.
+ * "OnlineNQ": rcu_barrier_callback() found online CPU, no callbacks.
+ * "IRQ": An rcu_barrier_callback() callback posted on remote CPU.
+ * "CB": An rcu_barrier_callback() invoked a callback, not the last.
+ * "LastCB": An rcu_barrier_callback() invoked the last callback.
+ * "Inc2": rcu_barrier_callback() piggyback check counter incremented.
+ * The "cpu" argument is the CPU or -1 if meaningless, the "cnt" argument
+ * is the count of remaining callbacks, and "done" is the piggybacking count.
+ */
+TRACE_EVENT(rcu_barrier,
+
+ TP_PROTO(char *rcuname, char *s, int cpu, int cnt, unsigned long done),
+
+ TP_ARGS(rcuname, s, cpu, cnt, done),
+
+ TP_STRUCT__entry(
+ __field(char *, rcuname)
+ __field(char *, s)
+ __field(int, cpu)
+ __field(int, cnt)
+ __field(unsigned long, done)
+ ),
+
+ TP_fast_assign(
+ __entry->rcuname = rcuname;
+ __entry->s = s;
+ __entry->cpu = cpu;
+ __entry->cnt = cnt;
+ __entry->done = done;
+ ),
+
+ TP_printk("%s %s cpu %d remaining %d # %lu",
+ __entry->rcuname, __entry->s, __entry->cpu, __entry->cnt,
+ __entry->done)
+);
+
#else /* #ifdef CONFIG_RCU_TRACE */

#define trace_rcu_grace_period(rcuname, gpnum, gpevent) do { } while (0)
@@ -563,6 +607,7 @@ TRACE_EVENT(rcu_torture_read,
#define trace_rcu_batch_end(rcuname, callbacks_invoked, cb, nr, iit, risk) \
do { } while (0)
#define trace_rcu_torture_read(rcutorturename, rhp) do { } while (0)
+#define trace_rcu_barrier(name, s, cpu, cnt, done) do { } while (0)

#endif /* #else #ifdef CONFIG_RCU_TRACE */

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index b0f1ab0..5c1c6ae 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -2257,6 +2257,17 @@ static int rcu_cpu_has_callbacks(int cpu)
}

/*
+ * Helper function for _rcu_barrier() tracing. If tracing is disabled,
+ * the compiler is expected to optimize this away.
+ */
+static void _rcu_barrier_trace(struct rcu_state *rsp, char *s,
+ int cpu, unsigned long done)
+{
+ trace_rcu_barrier(rsp->name, s, cpu,
+ atomic_read(&rsp->barrier_cpu_count), done);
+}
+
+/*
* RCU callback function for _rcu_barrier(). If we are last, wake
* up the task executing _rcu_barrier().
*/
@@ -2265,8 +2276,12 @@ static void rcu_barrier_callback(struct rcu_head *rhp)
struct rcu_data *rdp = container_of(rhp, struct rcu_data, barrier_head);
struct rcu_state *rsp = rdp->rsp;

- if (atomic_dec_and_test(&rsp->barrier_cpu_count))
+ if (atomic_dec_and_test(&rsp->barrier_cpu_count)) {
+ _rcu_barrier_trace(rsp, "LastCB", -1, rsp->n_barrier_done);
complete(&rsp->barrier_completion);
+ } else {
+ _rcu_barrier_trace(rsp, "CB", -1, rsp->n_barrier_done);
+ }
}

/*
@@ -2277,6 +2292,7 @@ static void rcu_barrier_func(void *type)
struct rcu_state *rsp = type;
struct rcu_data *rdp = __this_cpu_ptr(rsp->rda);

+ _rcu_barrier_trace(rsp, "IRQ", -1, rsp->n_barrier_done);
atomic_inc(&rsp->barrier_cpu_count);
rsp->call(&rdp->barrier_head, rcu_barrier_callback);
}
@@ -2295,6 +2311,7 @@ static void _rcu_barrier(struct rcu_state *rsp)
unsigned long snap_done;

init_rcu_head_on_stack(&rd.barrier_head);
+ _rcu_barrier_trace(rsp, "Begin", -1, snap);

/* Take mutex to serialize concurrent rcu_barrier() requests. */
mutex_lock(&rsp->barrier_mutex);
@@ -2312,7 +2329,9 @@ static void _rcu_barrier(struct rcu_state *rsp)
* value up to the next even number and adds two before comparing.
*/
snap_done = ACCESS_ONCE(rsp->n_barrier_done);
+ _rcu_barrier_trace(rsp, "Check", -1, snap_done);
if (ULONG_CMP_GE(snap_done, ((snap + 1) & ~0x1) + 2)) {
+ _rcu_barrier_trace(rsp, "EarlyExit", -1, snap_done);
smp_mb(); /* caller's subsequent code after above check. */
mutex_unlock(&rsp->barrier_mutex);
return;
@@ -2325,6 +2344,7 @@ static void _rcu_barrier(struct rcu_state *rsp)
*/
ACCESS_ONCE(rsp->n_barrier_done)++;
WARN_ON_ONCE((rsp->n_barrier_done & 0x1) != 1);
+ _rcu_barrier_trace(rsp, "Inc1", -1, rsp->n_barrier_done);
smp_mb(); /* Order ->n_barrier_done increment with below mechanism. */

/*
@@ -2361,13 +2381,19 @@ static void _rcu_barrier(struct rcu_state *rsp)
preempt_disable();
rdp = per_cpu_ptr(rsp->rda, cpu);
if (cpu_is_offline(cpu)) {
+ _rcu_barrier_trace(rsp, "Offline", cpu,
+ rsp->n_barrier_done);
preempt_enable();
while (cpu_is_offline(cpu) && ACCESS_ONCE(rdp->qlen))
schedule_timeout_interruptible(1);
} else if (ACCESS_ONCE(rdp->qlen)) {
+ _rcu_barrier_trace(rsp, "OnlineQ", cpu,
+ rsp->n_barrier_done);
smp_call_function_single(cpu, rcu_barrier_func, rsp, 1);
preempt_enable();
} else {
+ _rcu_barrier_trace(rsp, "OnlineNQ", cpu,
+ rsp->n_barrier_done);
preempt_enable();
}
}
@@ -2400,6 +2426,7 @@ static void _rcu_barrier(struct rcu_state *rsp)
smp_mb(); /* Keep increment after above mechanism. */
ACCESS_ONCE(rsp->n_barrier_done)++;
WARN_ON_ONCE((rsp->n_barrier_done & 0x1) != 0);
+ _rcu_barrier_trace(rsp, "Inc2", -1, rsp->n_barrier_done);
smp_mb(); /* Keep increment before caller's subsequent code. */

/* Wait for all rcu_barrier_callback() callbacks to be invoked. */
--
1.7.8


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