diff --git a/fs/ceph/debugfs.c b/fs/ceph/debugfs.c
index 00c39a2..7c95ae5 100644
--- a/fs/ceph/debugfs.c
+++ b/fs/ceph/debugfs.c
@@ -124,13 +124,15 @@ static int mdsc_show(struct seq_file *s, void *p)
 	return 0;
 }
 
-static s64 get_avg(struct percpu_counter *totalp, struct percpu_counter *sump,
+static s64 get_avg(atomic64_t *totalp, atomic64_t *sump, spinlock_t *lockp,
 		   s64 *total)
 {
 	s64 t, sum, avg = 0;
 
-	t = percpu_counter_sum(totalp);
-	sum = percpu_counter_sum(sump);
+	spin_lock(lockp);
+	t = atomic64_read(totalp);
+	sum = atomic64_read(sump);
+	spin_unlock(lockp);
 
 	if (likely(t))
 		avg = DIV64_U64_ROUND_CLOSEST(sum, t);
@@ -139,13 +141,22 @@ static s64 get_avg(struct percpu_counter *totalp, struct percpu_counter *sump,
 	return avg;
 }
 
-#define CEPH_METRIC_SHOW(name, total, avg, min, max) {		\
-	s64 _avg, _min, _max;					\
-	_avg = jiffies_to_usecs(avg);				\
-	_min = jiffies_to_usecs(min == S64_MAX ? 0 : min);	\
-	_max = jiffies_to_usecs(max);				\
-	seq_printf(s, "%-14s%-12lld%-16lld%-16lld%lld\n",	\
-		   name, total, _avg, _min, _max);		\
+#define CEPH_METRIC_SHOW(name, total, avg, min, max, sq) {		\
+	s64 _total, _avg, _min, _max, _sq, _st, _re = 0;		\
+	_avg = jiffies_to_usecs(avg);					\
+	_min = jiffies_to_usecs(min == S64_MAX ? 0 : min);		\
+	_max = jiffies_to_usecs(max);					\
+	_total = total - 1;						\
+	_sq = _total > 0 ? DIV64_U64_ROUND_CLOSEST(sq, _total) : 0;	\
+	_sq = jiffies_to_usecs(_sq);					\
+	_st = int_sqrt64(_sq);						\
+	if (_st > 0) {							\
+		_re = 5 * (_sq - (_st * _st));				\
+		_re = _re > 0 ? _re - 1 : 0;				\
+		_re = _st > 0 ? div64_s64(_re, _st) : 0;		\
+	}								\
+	seq_printf(s, "%-14s%-12lld%-16lld%-16lld%-16lld%lld.%lld\n",	\
+		   name, total, _avg, _min, _max, _st, _re);		\
 }
 
 static int metric_show(struct seq_file *s, void *p)
@@ -154,31 +165,37 @@ static int metric_show(struct seq_file *s, void *p)
 	struct ceph_mds_client *mdsc = fsc->mdsc;
 	struct ceph_client_metric *m = &mdsc->metric;
 	int i, nr_caps = 0;
-	s64 total, avg, min, max;
+	s64 total, avg, min, max, sq;
 
-	seq_printf(s, "item          total       avg_lat(us)     min_lat(us)     max_lat(us)\n");
-	seq_printf(s, "---------------------------------------------------------------------\n");
+	seq_printf(s, "item          total       avg_lat(us)     min_lat(us)     max_lat(us)     stdev(us)\n");
+	seq_printf(s, "-----------------------------------------------------------------------------------\n");
 
 	avg = get_avg(&mdsc->metric.total_reads,
 		      &mdsc->metric.read_latency_sum,
+		      &mdsc->metric.read_latency_lock,
 		      &total);
-	min = atomic64_read(&m->read_latency_min);
-	max = atomic64_read(&m->read_latency_max);
-	CEPH_METRIC_SHOW("read", total, avg, min, max);
+	min = atomic64_read(&mdsc->metric.read_latency_min);
+	max = atomic64_read(&mdsc->metric.read_latency_max);
+	sq = percpu_counter_sum(&mdsc->metric.read_latency_sq_sum);
+	CEPH_METRIC_SHOW("read", total, avg, min, max, sq);
 
 	avg = get_avg(&mdsc->metric.total_writes,
 		      &mdsc->metric.write_latency_sum,
+		      &mdsc->metric.write_latency_lock,
 		      &total);
-	min = atomic64_read(&m->write_latency_min);
-	max = atomic64_read(&m->write_latency_max);
-	CEPH_METRIC_SHOW("write", total, avg, min, max);
+	min = atomic64_read(&mdsc->metric.write_latency_min);
+	max = atomic64_read(&mdsc->metric.write_latency_max);
+	sq = percpu_counter_sum(&mdsc->metric.write_latency_sq_sum);
+	CEPH_METRIC_SHOW("write", total, avg, min, max, sq);
 
 	avg = get_avg(&mdsc->metric.total_metadatas,
 		      &mdsc->metric.metadata_latency_sum,
+		      &mdsc->metric.metadata_latency_lock,
 		      &total);
-	min = atomic64_read(&m->metadata_latency_min);
-	max = atomic64_read(&m->metadata_latency_max);
-	CEPH_METRIC_SHOW("metadata", total, avg, min, max);
+	min = atomic64_read(&mdsc->metric.metadata_latency_min);
+	max = atomic64_read(&mdsc->metric.metadata_latency_max);
+	sq = percpu_counter_sum(&mdsc->metric.metadata_latency_sq_sum);
+	CEPH_METRIC_SHOW("metadata", total, avg, min, max, sq);
 
 	seq_printf(s, "\n");
 	seq_printf(s, "item          total           miss            hit\n");
diff --git a/fs/ceph/metric.c b/fs/ceph/metric.c
index c0158f6..ac1e800 100644
--- a/fs/ceph/metric.c
+++ b/fs/ceph/metric.c
@@ -2,6 +2,7 @@
 
 #include <linux/types.h>
 #include <linux/percpu_counter.h>
+#include <linux/math64.h>
 
 #include "metric.h"
 
@@ -29,52 +30,43 @@ int ceph_metric_init(struct ceph_client_metric *m)
 	if (ret)
 		goto err_i_caps_mis;
 
-	ret = percpu_counter_init(&m->total_reads, 0, GFP_KERNEL);
+	ret = percpu_counter_init(&m->read_latency_sq_sum, 0, GFP_KERNEL);
 	if (ret)
-		goto err_total_reads;
-
-	ret = percpu_counter_init(&m->read_latency_sum, 0, GFP_KERNEL);
-	if (ret)
-		goto err_read_latency_sum;
+		goto err_read_latency_sq_sum;
 
+	spin_lock_init(&m->read_latency_lock);
+	atomic64_set(&m->total_reads, 0);
+	atomic64_set(&m->read_latency_sum, 0);
 	atomic64_set(&m->read_latency_min, S64_MAX);
 	atomic64_set(&m->read_latency_max, 0);
 
-	ret = percpu_counter_init(&m->total_writes, 0, GFP_KERNEL);
+	ret = percpu_counter_init(&m->write_latency_sq_sum, 0, GFP_KERNEL);
 	if (ret)
-		goto err_total_writes;
-
-	ret = percpu_counter_init(&m->write_latency_sum, 0, GFP_KERNEL);
-	if (ret)
-		goto err_write_latency_sum;
+		goto err_write_latency_sq_sum;
 
+	spin_lock_init(&m->write_latency_lock);
+	atomic64_set(&m->total_writes, 0);
+	atomic64_set(&m->write_latency_sum, 0);
 	atomic64_set(&m->write_latency_min, S64_MAX);
 	atomic64_set(&m->write_latency_max, 0);
 
-	ret = percpu_counter_init(&m->total_metadatas, 0, GFP_KERNEL);
-	if (ret)
-		goto err_total_metadatas;
-
-	ret = percpu_counter_init(&m->metadata_latency_sum, 0, GFP_KERNEL);
+	ret = percpu_counter_init(&m->metadata_latency_sq_sum, 0, GFP_KERNEL);
 	if (ret)
-		goto err_metadata_latency_sum;
+		goto err_metadata_latency_sq_sum;
 
+	spin_lock_init(&m->metadata_latency_lock);
+	atomic64_set(&m->total_metadatas, 0);
+	atomic64_set(&m->metadata_latency_sum, 0);
 	atomic64_set(&m->metadata_latency_min, S64_MAX);
 	atomic64_set(&m->metadata_latency_max, 0);
 
 	return 0;
 
-err_metadata_latency_sum:
-	percpu_counter_destroy(&m->total_metadatas);
-err_total_metadatas:
-	percpu_counter_destroy(&m->write_latency_sum);
-err_write_latency_sum:
-	percpu_counter_destroy(&m->total_writes);
-err_total_writes:
-	percpu_counter_destroy(&m->read_latency_sum);
-err_read_latency_sum:
-	percpu_counter_destroy(&m->total_reads);
-err_total_reads:
+err_metadata_latency_sq_sum:
+	percpu_counter_destroy(&m->write_latency_sq_sum);
+err_write_latency_sq_sum:
+	percpu_counter_destroy(&m->read_latency_sq_sum);
+err_read_latency_sq_sum:
 	percpu_counter_destroy(&m->i_caps_mis);
 err_i_caps_mis:
 	percpu_counter_destroy(&m->i_caps_hit);
@@ -91,14 +83,111 @@ void ceph_metric_destroy(struct ceph_client_metric *m)
 	if (!m)
 		return;
 
-	percpu_counter_destroy(&m->metadata_latency_sum);
-	percpu_counter_destroy(&m->total_metadatas);
-	percpu_counter_destroy(&m->write_latency_sum);
-	percpu_counter_destroy(&m->total_writes);
-	percpu_counter_destroy(&m->read_latency_sum);
-	percpu_counter_destroy(&m->total_reads);
+	percpu_counter_destroy(&m->metadata_latency_sq_sum);
+	percpu_counter_destroy(&m->write_latency_sq_sum);
+	percpu_counter_destroy(&m->read_latency_sq_sum);
 	percpu_counter_destroy(&m->i_caps_mis);
 	percpu_counter_destroy(&m->i_caps_hit);
 	percpu_counter_destroy(&m->d_lease_mis);
 	percpu_counter_destroy(&m->d_lease_hit);
 }
+
+static inline void __update_min_latency(atomic64_t *min, unsigned long lat)
+{
+	unsigned long cur, old;
+
+	cur = atomic64_read(min);
+	do {
+		old = cur;
+		if (likely(lat >= old))
+			break;
+	} while (unlikely((cur = atomic64_cmpxchg(min, old, lat)) != old));
+}
+
+static inline void __update_max_latency(atomic64_t *max, unsigned long lat)
+{
+	unsigned long cur, old;
+
+	cur = atomic64_read(max);
+	do {
+		old = cur;
+		if (likely(lat <= old))
+			break;
+	} while (unlikely((cur = atomic64_cmpxchg(max, old, lat)) != old));
+}
+
+static inline void __update_avg_and_sq(atomic64_t *totalp, atomic64_t *lat_sump,
+				       struct percpu_counter *sq_sump,
+				       spinlock_t *lockp, unsigned long lat)
+{
+	s64 total, avg, sq, lsum;
+
+	spin_lock(lockp);
+	total = atomic64_inc_return(totalp);
+	lsum = atomic64_add_return(lat, lat_sump);
+	spin_unlock(lockp);
+
+	if (unlikely(total == 1))
+		return;
+
+	/* the sq is (lat - old_avg) * (lat - new_avg) */
+	avg = DIV64_U64_ROUND_CLOSEST((lsum - lat), (total - 1));
+	sq = lat - avg;
+	avg = DIV64_U64_ROUND_CLOSEST(lsum, total);
+	sq = sq * (lat - avg);
+	percpu_counter_add(sq_sump, sq);
+}
+
+void ceph_update_read_latency(struct ceph_client_metric *m,
+			      unsigned long r_start,
+			      unsigned long r_end,
+			      int rc)
+{
+	unsigned long lat = r_end - r_start;
+
+	if (rc < 0 && rc != -ENOENT && rc != -ETIMEDOUT)
+		return;
+
+	__update_min_latency(&m->read_latency_min, lat);
+	__update_max_latency(&m->read_latency_max, lat);
+	__update_avg_and_sq(&m->total_reads, &m->read_latency_sum,
+			    &m->read_latency_sq_sum,
+			    &m->read_latency_lock,
+			    lat);
+}
+
+void ceph_update_write_latency(struct ceph_client_metric *m,
+			       unsigned long r_start,
+			       unsigned long r_end,
+			       int rc)
+{
+	unsigned long lat = r_end - r_start;
+
+	if (rc && rc != -ETIMEDOUT)
+		return;
+
+	__update_min_latency(&m->write_latency_min, lat);
+	__update_max_latency(&m->write_latency_max, lat);
+	__update_avg_and_sq(&m->total_writes, &m->write_latency_sum,
+			    &m->write_latency_sq_sum,
+			    &m->write_latency_lock,
+			    lat);
+}
+
+void ceph_update_metadata_latency(struct ceph_client_metric *m,
+				  unsigned long r_start,
+				  unsigned long r_end,
+				  int rc)
+{
+	unsigned long lat = r_end - r_start;
+
+	if (rc && rc != -ENOENT)
+		return;
+
+	__update_min_latency(&m->metadata_latency_min, lat);
+	__update_max_latency(&m->metadata_latency_max, lat);
+	__update_avg_and_sq(&m->total_metadatas, &m->metadata_latency_sum,
+			    &m->metadata_latency_sq_sum,
+			    &m->metadata_latency_lock,
+			    lat);
+}
diff --git a/fs/ceph/metric.h b/fs/ceph/metric.h
index 3f90875..fc1ffb1 100644
--- a/fs/ceph/metric.h
+++ b/fs/ceph/metric.h
@@ -14,18 +14,24 @@ struct ceph_client_metric {
 	struct percpu_counter i_caps_hit;
 	struct percpu_counter i_caps_mis;
 
-	struct percpu_counter total_reads;
-	struct percpu_counter read_latency_sum;
+	struct percpu_counter read_latency_sq_sum;
+	spinlock_t read_latency_lock;
+	atomic64_t total_reads;
+	atomic64_t read_latency_sum;
 	atomic64_t read_latency_min;
 	atomic64_t read_latency_max;
 
-	struct percpu_counter total_writes;
-	struct percpu_counter write_latency_sum;
+	struct percpu_counter write_latency_sq_sum;
+	spinlock_t write_latency_lock;
+	atomic64_t total_writes;
+	atomic64_t write_latency_sum;
 	atomic64_t write_latency_min;
 	atomic64_t write_latency_max;
 
-	struct percpu_counter total_metadatas;
-	struct percpu_counter metadata_latency_sum;
+	struct percpu_counter metadata_latency_sq_sum;
+	spinlock_t metadata_latency_lock;
+	atomic64_t total_metadatas;
+	atomic64_t metadata_latency_sum;
 	atomic64_t metadata_latency_min;
 	atomic64_t metadata_latency_max;
 };
@@ -43,75 +49,16 @@ static inline void ceph_update_cap_mis(struct ceph_client_metric *m)
 	percpu_counter_inc(&m->i_caps_mis);
 }
 
-static inline void __update_min_latency(atomic64_t *min, unsigned long lat)
-{
-	unsigned long cur, old;
-
-	cur = atomic64_read(min);
-	do {
-		old = cur;
-		if (likely(lat >= old))
-			break;
-	} while (unlikely((cur = atomic64_cmpxchg(min, old, lat)) != old));
-}
-
-static inline void __update_max_latency(atomic64_t *max, unsigned long lat)
-{
-	unsigned long cur, old;
-
-	cur = atomic64_read(max);
-	do {
-		old = cur;
-		if (likely(lat <= old))
-			break;
-	} while (unlikely((cur = atomic64_cmpxchg(max, old, lat)) != old));
-}
-
-static inline void ceph_update_read_latency(struct ceph_client_metric *m,
-					    unsigned long r_start,
-					    unsigned long r_end,
-					    int rc)
-{
-	unsigned long lat = r_end - r_start;
-
-	if (rc < 0 && rc != -ENOENT && rc != -ETIMEDOUT)
-		return;
-
-	percpu_counter_inc(&m->total_reads);
-	percpu_counter_add(&m->read_latency_sum, lat);
-	__update_min_latency(&m->read_latency_min, lat);
-	__update_max_latency(&m->read_latency_max, lat);
-}
-
-static inline void ceph_update_write_latency(struct ceph_client_metric *m,
-					     unsigned long r_start,
-					     unsigned long r_end,
-					     int rc)
-{
-	unsigned long lat = r_end - r_start;
-
-	if (rc && rc != -ETIMEDOUT)
-		return;
-
-	percpu_counter_inc(&m->total_writes);
-	percpu_counter_add(&m->write_latency_sum, lat);
-	__update_min_latency(&m->write_latency_min, lat);
-	__update_max_latency(&m->write_latency_max, lat);
-}
-
-static inline void ceph_update_metadata_latency(struct ceph_client_metric *m,
-						unsigned long r_start,
-						unsigned long r_end,
-						int rc)
-{
-	unsigned long lat = r_end - r_start;
-
-	if (rc && rc != -ENOENT)
-		return;
-
-	percpu_counter_inc(&m->total_metadatas);
-	percpu_counter_add(&m->metadata_latency_sum, lat);
-	__update_min_latency(&m->metadata_latency_min, lat);
-	__update_max_latency(&m->metadata_latency_max, lat);
-}
+extern void ceph_update_read_latency(struct ceph_client_metric *m,
+				     unsigned long r_start,
+				     unsigned long r_end,
+				     int rc);
+extern void ceph_update_write_latency(struct ceph_client_metric *m,
+				      unsigned long r_start,
+				      unsigned long r_end,
+				      int rc);
+extern void ceph_update_metadata_latency(struct ceph_client_metric *m,
+					 unsigned long r_start,
+					 unsigned long r_end,
+					 int rc);
 #endif /* _FS_CEPH_MDS_METRIC_H */
