uses nanos precision for timestamp when submitting metrics to influxdb (#20623)

Current datapoint_info! is apparently overwriting itself when run inside
a loop. For example in
https://github.com/solana-labs/solana/blob/005d6863f/core/src/window_service.rs#L101-L107
only one of the slots will show up in influxdb.

This is apparently because of metrics code using milliseconds as the
timestamp, as mentioned here:
https://github.com/solana-labs/solana/issues/19789#issuecomment-922482013

metrics/src/metrics.rs

@@ -1,20 +1,23 @@
 //! The `metrics` module enables sending measurements to an `InfluxDB` instance
 
-use crate::{counter::CounterPoint, datapoint::DataPoint};
-use gethostname::gethostname;
-use lazy_static::lazy_static;
-use log::*;
-use solana_sdk::hash::hash;
-use std::{
-    collections::HashMap,
-    convert::Into,
-    sync::{
-        mpsc::{channel, Receiver, RecvTimeoutError, Sender},
-        Arc, Barrier, Mutex, Once, RwLock,
+use {
+    crate::{counter::CounterPoint, datapoint::DataPoint},
+    gethostname::gethostname,
+    lazy_static::lazy_static,
+    log::*,
+    solana_sdk::hash::hash,
+    std::{
+        cmp,
+        collections::HashMap,
+        convert::Into,
+        env,
+        sync::{
+            mpsc::{channel, Receiver, RecvTimeoutError, Sender},
+            Arc, Barrier, Mutex, Once, RwLock,
+        },
+        thread,
+        time::{Duration, Instant, UNIX_EPOCH},
     },
-    thread,
-    time::{Duration, Instant},
-    {cmp, env},
 };
 
 type CounterMap = HashMap<(&'static str, u64), CounterPoint>;
@@ -68,7 +71,7 @@ impl InfluxDbMetricsWriter {
         );
 
         let write_url = format!(
-            "{}/write?db={}&u={}&p={}&precision=ms",
+            "{}/write?db={}&u={}&p={}&precision=n",
             &config.host, &config.db, &config.username, &config.password
         );
 
@@ -97,8 +100,9 @@ impl MetricsWriter for InfluxDbMetricsWriter {
                     ));
                     first = false;
                 }
-
-                line.push_str(&format!(" {}\n", &point.timestamp));
+                let timestamp = point.timestamp.duration_since(UNIX_EPOCH);
+                let nanos = timestamp.unwrap().as_nanos();
+                line.push_str(&format!(" {}\n", nanos));
             }
 
             let client = reqwest::blocking::Client::builder()
@@ -537,7 +541,7 @@ mod test {
                 CounterPoint {
                     name: "counter",
                     count: 10,
-                    timestamp: 0,
+                    timestamp: UNIX_EPOCH,
                 },
                 Level::Info,
                 0, // use the same bucket