Re: [PATCH v3] ceph: add min/max latency support for read/write/metadata metrics

Xiubo Li <xiubli@xxxxxxxxxx> · Tue, 17 Mar 2020 19:33:50 +0800

On 2020/3/17 19:12, Jeff Layton wrote:
On Mon, 2020-03-16 at 20:00 -0400, xiubli@xxxxxxxxxx wrote:
From: Xiubo Li <xiubli@xxxxxxxxxx>

These will be very useful help diagnose problems.

URL: https://tracker.ceph.com/issues/44533
Signed-off-by: Xiubo Li <xiubli@xxxxxxxxxx>
---

Changed in V2:
- switch spin lock to cmpxchg

Changed in V3:
- add the __update_min/max_latency helpers
- minor fix

  fs/ceph/debugfs.c    | 26 +++++++++++++++++++++-----
  fs/ceph/mds_client.c |  9 +++++++++
  fs/ceph/metric.h     | 52 +++++++++++++++++++++++++++++++++++++++++++++++++---
  3 files changed, 79 insertions(+), 8 deletions(-)

diff --git a/fs/ceph/debugfs.c b/fs/ceph/debugfs.c
index 60f3e307..bcf7215 100644
--- a/fs/ceph/debugfs.c
+++ b/fs/ceph/debugfs.c
@@ -130,27 +130,43 @@ static int metric_show(struct seq_file *s, void *p)
  	struct ceph_mds_client *mdsc = fsc->mdsc;
  	int i, nr_caps = 0;
  	s64 total, sum, avg = 0;
+	unsigned long min, max;
  
-	seq_printf(s, "item          total       sum_lat(us)     avg_lat(us)\n");
-	seq_printf(s, "-----------------------------------------------------\n");
+	seq_printf(s, "item          total       sum_lat(us)     avg_lat(us)     min_lat(us)     max_lat(us)\n");
+	seq_printf(s, "-------------------------------------------------------------------------------------\n");
  
  	total = percpu_counter_sum(&mdsc->metric.total_reads);
  	sum = percpu_counter_sum(&mdsc->metric.read_latency_sum);
  	sum = jiffies_to_usecs(sum);
  	avg = total ? sum / total : 0;
-	seq_printf(s, "%-14s%-12lld%-16lld%lld\n", "read", total, sum, avg);
+	min = atomic_long_read(&mdsc->metric.read_latency_min);
+	min = jiffies_to_usecs(min == ULONG_MAX ? 0 : min);
+	max = atomic_long_read(&mdsc->metric.read_latency_max);
+	max = jiffies_to_usecs(max);
+	seq_printf(s, "%-14s%-12lld%-16lld%-16lld%-16ld%ld\n", "read",
+		   total, sum, avg, min, max);
  
  	total = percpu_counter_sum(&mdsc->metric.total_writes);
  	sum = percpu_counter_sum(&mdsc->metric.write_latency_sum);
  	sum = jiffies_to_usecs(sum);
  	avg = total ? sum / total : 0;
-	seq_printf(s, "%-14s%-12lld%-16lld%lld\n", "write", total, sum, avg);
+	min = atomic_long_read(&mdsc->metric.write_latency_min);
+	min = jiffies_to_usecs(min == ULONG_MAX ? 0 : min);
+	max = atomic_long_read(&mdsc->metric.write_latency_max);
+	max = jiffies_to_usecs(max);
+	seq_printf(s, "%-14s%-12lld%-16lld%-16lld%-16ld%ld\n", "write",
+		   total, sum, avg, min, max);
  
  	total = percpu_counter_sum(&mdsc->metric.total_metadatas);
  	sum = percpu_counter_sum(&mdsc->metric.metadata_latency_sum);
  	sum = jiffies_to_usecs(sum);
  	avg = total ? sum / total : 0;
-	seq_printf(s, "%-14s%-12lld%-16lld%lld\n", "metadata", total, sum, avg);
+	min = atomic_long_read(&mdsc->metric.metadata_latency_min);
+	min = jiffies_to_usecs(min == ULONG_MAX ? 0 : min);
+	max = atomic_long_read(&mdsc->metric.metadata_latency_max);
+	max = jiffies_to_usecs(max);
+	seq_printf(s, "%-14s%-12lld%-16lld%-16lld%-16ld%ld\n", "metadata",
+		   total, sum, avg, min, max);
  
  	seq_printf(s, "\n");
  	seq_printf(s, "item          total           miss            hit\n");
diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c
index 5c03ed3..7844aa6 100644
--- a/fs/ceph/mds_client.c
+++ b/fs/ceph/mds_client.c
@@ -4358,6 +4358,9 @@ static int ceph_mdsc_metric_init(struct ceph_client_metric *metric)
  	if (ret)
  		goto err_read_latency_sum;
  
+	atomic_long_set(&metric->read_latency_min, ULONG_MAX);
+	atomic_long_set(&metric->read_latency_max, 0);
+
  	ret = percpu_counter_init(&metric->total_writes, 0, GFP_KERNEL);
  	if (ret)
  		goto err_total_writes;
@@ -4366,6 +4369,9 @@ static int ceph_mdsc_metric_init(struct ceph_client_metric *metric)
  	if (ret)
  		goto err_write_latency_sum;
  
+	atomic_long_set(&metric->write_latency_min, ULONG_MAX);
+	atomic_long_set(&metric->write_latency_max, 0);
+
  	ret = percpu_counter_init(&metric->total_metadatas, 0, GFP_KERNEL);
  	if (ret)
  		goto err_total_metadatas;
@@ -4374,6 +4380,9 @@ static int ceph_mdsc_metric_init(struct ceph_client_metric *metric)
  	if (ret)
  		goto err_metadata_latency_sum;
  
+	atomic_long_set(&metric->metadata_latency_min, ULONG_MAX);
+	atomic_long_set(&metric->metadata_latency_max, 0);
+
  	return 0;
  
  err_metadata_latency_sum:
diff --git a/fs/ceph/metric.h b/fs/ceph/metric.h
index faba142..c9c76d5 100644
--- a/fs/ceph/metric.h
+++ b/fs/ceph/metric.h
@@ -2,6 +2,10 @@
  #ifndef _FS_CEPH_MDS_METRIC_H
  #define _FS_CEPH_MDS_METRIC_H
  
+#include <linux/atomic.h>
+#include <linux/percpu.h>
+#include <linux/spinlock.h>
+
  /* This is the global metrics */
  struct ceph_client_metric {
  	atomic64_t            total_dentries;
@@ -13,12 +17,18 @@ struct ceph_client_metric {
  
  	struct percpu_counter total_reads;
  	struct percpu_counter read_latency_sum;
+	atomic_long_t read_latency_min;
+	atomic_long_t read_latency_max;
  
  	struct percpu_counter total_writes;
  	struct percpu_counter write_latency_sum;
+	atomic_long_t write_latency_min;
+	atomic_long_t write_latency_max;
  
  	struct percpu_counter total_metadatas;
  	struct percpu_counter metadata_latency_sum;
+	atomic_long_t metadata_latency_min;
+	atomic_long_t metadata_latency_max;
  };
  
  static inline void ceph_update_cap_hit(struct ceph_client_metric *m)
@@ -31,16 +41,44 @@ 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(atomic_long_t *min, unsigned long lat)
nit: I don't see a need for the double-underscore prefix here.

+{
+	unsigned long cur, old;
+
+	cur = atomic_long_read(min);
+	do {
+		old = cur;
+		if (likely(lat >= old))
+			break;
+	} while ((cur = atomic_long_cmpxchg(min, old, lat)) != old);
+}
+
+static inline void __update_max_latency(atomic_long_t *max, unsigned long lat)
+{
+	unsigned long cur, old;
+
+	cur = atomic_long_read(max);
+	do {
+		old = cur;
+		if (likely(lat <= old))
+			break;
+	} while ((cur = atomic_long_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, r_end - r_start);
+	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,
@@ -48,11 +86,15 @@ static inline void ceph_update_write_latency(struct ceph_client_metric *m,
  					     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, r_end - r_start);
+	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,
@@ -60,10 +102,14 @@ static inline void ceph_update_metadata_latency(struct ceph_client_metric *m,
  						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, r_end - r_start);
+	percpu_counter_add(&m->metadata_latency_sum, lat);
+	__update_min_latency(&m->metadata_latency_min, lat);
+	__update_max_latency(&m->metadata_latency_max, lat);
  }
  #endif /* _FS_CEPH_MDS_METRIC_H */
Looks good overall though.

Note that this makes your stddev patches no longer merge cleanly.
They'll need to be rebased on top of this patch. Maybe send it
altogether as a series since there are dependencies here?

Sure, will post the V4 later.

Thanks


Thanks,








