On 9/14/21 4:49 PM, Venky Shankar wrote:
The math involved in tracking average and standard deviation
for r/w/m latencies looks incorrect. Fix that up. Also, change
the variable name that tracks standard deviation (*_sq_sum) to
*_stdev.
Signed-off-by: Venky Shankar <vshankar@xxxxxxxxxx>
---
fs/ceph/debugfs.c | 14 +++++-----
fs/ceph/metric.c | 70 ++++++++++++++++++++++-------------------------
fs/ceph/metric.h | 9 ++++--
3 files changed, 45 insertions(+), 48 deletions(-)
diff --git a/fs/ceph/debugfs.c b/fs/ceph/debugfs.c
index 38b78b45811f..3abfa7ae8220 100644
--- a/fs/ceph/debugfs.c
+++ b/fs/ceph/debugfs.c
@@ -152,7 +152,7 @@ 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 nr_caps = 0;
- s64 total, sum, avg, min, max, sq;
+ s64 total, sum, avg, min, max, stdev;
u64 sum_sz, avg_sz, min_sz, max_sz;
sum = percpu_counter_sum(&m->total_inodes);
@@ -175,9 +175,9 @@ static int metric_show(struct seq_file *s, void *p)
avg = total > 0 ? DIV64_U64_ROUND_CLOSEST(sum, total) : 0;
min = m->read_latency_min;
max = m->read_latency_max;
- sq = m->read_latency_sq_sum;
+ stdev = m->read_latency_stdev;
spin_unlock(&m->read_metric_lock);
- CEPH_LAT_METRIC_SHOW("read", total, avg, min, max, sq);
+ CEPH_LAT_METRIC_SHOW("read", total, avg, min, max, stdev);
spin_lock(&m->write_metric_lock);
total = m->total_writes;
@@ -185,9 +185,9 @@ static int metric_show(struct seq_file *s, void *p)
avg = total > 0 ? DIV64_U64_ROUND_CLOSEST(sum, total) : 0;
min = m->write_latency_min;
max = m->write_latency_max;
- sq = m->write_latency_sq_sum;
+ stdev = m->write_latency_stdev;
spin_unlock(&m->write_metric_lock);
- CEPH_LAT_METRIC_SHOW("write", total, avg, min, max, sq);
+ CEPH_LAT_METRIC_SHOW("write", total, avg, min, max, stdev);
spin_lock(&m->metadata_metric_lock);
total = m->total_metadatas;
@@ -195,9 +195,9 @@ static int metric_show(struct seq_file *s, void *p)
avg = total > 0 ? DIV64_U64_ROUND_CLOSEST(sum, total) : 0;
min = m->metadata_latency_min;
max = m->metadata_latency_max;
- sq = m->metadata_latency_sq_sum;
+ stdev = m->metadata_latency_stdev;
spin_unlock(&m->metadata_metric_lock);
- CEPH_LAT_METRIC_SHOW("metadata", total, avg, min, max, sq);
+ CEPH_LAT_METRIC_SHOW("metadata", total, avg, min, max, stdev);
seq_printf(s, "\n");
seq_printf(s, "item total avg_sz(bytes) min_sz(bytes) max_sz(bytes) total_sz(bytes)\n");
diff --git a/fs/ceph/metric.c b/fs/ceph/metric.c
index 226dc38e2909..6b774b1a88ce 100644
--- a/fs/ceph/metric.c
+++ b/fs/ceph/metric.c
@@ -244,7 +244,8 @@ int ceph_metric_init(struct ceph_client_metric *m)
goto err_i_caps_mis;
spin_lock_init(&m->read_metric_lock);
- m->read_latency_sq_sum = 0;
+ m->read_latency_stdev = 0;
+ m->avg_read_latency = 0;
m->read_latency_min = KTIME_MAX;
m->read_latency_max = 0;
m->total_reads = 0;
@@ -254,7 +255,8 @@ int ceph_metric_init(struct ceph_client_metric *m)
m->read_size_sum = 0;
spin_lock_init(&m->write_metric_lock);
- m->write_latency_sq_sum = 0;
+ m->write_latency_stdev = 0;
+ m->avg_write_latency = 0;
m->write_latency_min = KTIME_MAX;
m->write_latency_max = 0;
m->total_writes = 0;
@@ -264,7 +266,8 @@ int ceph_metric_init(struct ceph_client_metric *m)
m->write_size_sum = 0;
spin_lock_init(&m->metadata_metric_lock);
- m->metadata_latency_sq_sum = 0;
+ m->metadata_latency_stdev = 0;
+ m->avg_metadata_latency = 0;
m->metadata_latency_min = KTIME_MAX;
m->metadata_latency_max = 0;
m->total_metadatas = 0;
@@ -322,20 +325,26 @@ void ceph_metric_destroy(struct ceph_client_metric *m)
max = new; \
}
-static inline void __update_stdev(ktime_t total, ktime_t lsum,
- ktime_t *sq_sump, ktime_t lat)
+static inline void __update_latency(ktime_t *ctotal, ktime_t *lsum,
+ ktime_t *lavg, ktime_t *min, ktime_t *max,
+ ktime_t *lstdev, ktime_t lat)
{
- ktime_t avg, sq;
+ ktime_t total, avg, stdev;
- if (unlikely(total == 1))
- return;
+ total = ++(*ctotal);
+ *lsum += lat;
+
+ METRIC_UPDATE_MIN_MAX(*min, *max, lat);
- /* 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);
- *sq_sump += sq;
+ if (unlikely(total == 1)) {
+ *lavg = lat;
+ *lstdev = 0;
+ } else {
+ avg = *lavg + div64_s64(lat - *lavg, total);
+ stdev = *lstdev + (lat - *lavg)*(lat - avg);
+ *lstdev = int_sqrt(div64_u64(stdev, total - 1));
In kernel space, won't it a little heavy to run the in_sqrt() every time
when updating the latency ?
@Jeff, any idea ?
+ *lavg = avg;
+ }
}
void ceph_update_read_metrics(struct ceph_client_metric *m,
@@ -343,23 +352,18 @@ void ceph_update_read_metrics(struct ceph_client_metric *m,
unsigned int size, int rc)
{
ktime_t lat = ktime_sub(r_end, r_start);
- ktime_t total;
if (unlikely(rc < 0 && rc != -ENOENT && rc != -ETIMEDOUT))
return;
spin_lock(&m->read_metric_lock);
- total = ++m->total_reads;
m->read_size_sum += size;
- m->read_latency_sum += lat;
METRIC_UPDATE_MIN_MAX(m->read_size_min,
m->read_size_max,
size);
- METRIC_UPDATE_MIN_MAX(m->read_latency_min,
- m->read_latency_max,
- lat);
- __update_stdev(total, m->read_latency_sum,
- &m->read_latency_sq_sum, lat);
+ __update_latency(&m->total_reads, &m->read_latency_sum,
+ &m->avg_read_latency, &m->read_latency_min,
+ &m->read_latency_max, &m->read_latency_stdev, lat);
spin_unlock(&m->read_metric_lock);
}
@@ -368,23 +372,18 @@ void ceph_update_write_metrics(struct ceph_client_metric *m,
unsigned int size, int rc)
{
ktime_t lat = ktime_sub(r_end, r_start);
- ktime_t total;
if (unlikely(rc && rc != -ETIMEDOUT))
return;
spin_lock(&m->write_metric_lock);
- total = ++m->total_writes;
m->write_size_sum += size;
- m->write_latency_sum += lat;
METRIC_UPDATE_MIN_MAX(m->write_size_min,
m->write_size_max,
size);
- METRIC_UPDATE_MIN_MAX(m->write_latency_min,
- m->write_latency_max,
- lat);
- __update_stdev(total, m->write_latency_sum,
- &m->write_latency_sq_sum, lat);
+ __update_latency(&m->total_writes, &m->write_latency_sum,
+ &m->avg_write_latency, &m->write_latency_min,
+ &m->write_latency_max, &m->write_latency_stdev, lat);
spin_unlock(&m->write_metric_lock);
}
@@ -393,18 +392,13 @@ void ceph_update_metadata_metrics(struct ceph_client_metric *m,
int rc)
{
ktime_t lat = ktime_sub(r_end, r_start);
- ktime_t total;
if (unlikely(rc && rc != -ENOENT))
return;
spin_lock(&m->metadata_metric_lock);
- total = ++m->total_metadatas;
- m->metadata_latency_sum += lat;
- METRIC_UPDATE_MIN_MAX(m->metadata_latency_min,
- m->metadata_latency_max,
- lat);
- __update_stdev(total, m->metadata_latency_sum,
- &m->metadata_latency_sq_sum, lat);
+ __update_latency(&m->total_metadatas, &m->metadata_latency_sum,
+ &m->avg_metadata_latency, &m->metadata_latency_min,
+ &m->metadata_latency_max, &m->metadata_latency_stdev, lat);
spin_unlock(&m->metadata_metric_lock);
}
diff --git a/fs/ceph/metric.h b/fs/ceph/metric.h
index 103ed736f9d2..a5da21b8f8ed 100644
--- a/fs/ceph/metric.h
+++ b/fs/ceph/metric.h
@@ -138,7 +138,8 @@ struct ceph_client_metric {
u64 read_size_min;
u64 read_size_max;
ktime_t read_latency_sum;
- ktime_t read_latency_sq_sum;
+ ktime_t avg_read_latency;
+ ktime_t read_latency_stdev;
ktime_t read_latency_min;
ktime_t read_latency_max;
@@ -148,14 +149,16 @@ struct ceph_client_metric {
u64 write_size_min;
u64 write_size_max;
ktime_t write_latency_sum;
- ktime_t write_latency_sq_sum;
+ ktime_t avg_write_latency;
+ ktime_t write_latency_stdev;
ktime_t write_latency_min;
ktime_t write_latency_max;
spinlock_t metadata_metric_lock;
u64 total_metadatas;
ktime_t metadata_latency_sum;
- ktime_t metadata_latency_sq_sum;
+ ktime_t avg_metadata_latency;
+ ktime_t metadata_latency_stdev;
ktime_t metadata_latency_min;
ktime_t metadata_latency_max;
