metrics: add H2 Histogram option to improve histogram granularity

spellcheck.dic

@@ -12,12 +12,15 @@
 0xA
 0xD
 100ms
+100ns
 10ms
 ~12
+12.5%
 ±1m
 ±1ms
 1ms
 1s
+25%
 250ms
 2x
 ~4
@@ -116,9 +119,11 @@ GID
 goroutines
 Growable
 gzip
+H2
 hashmaps
 HashMaps
 hashsets
+HdrHistogram
 ie
 Illumos
 impl

tokio/Cargo.toml

@@ -96,7 +96,7 @@ mio = { version = "1.0.1", optional = true, default-features = false }
 parking_lot = { version = "0.12.0", optional = true }
 
 [target.'cfg(not(target_family = "wasm"))'.dependencies]
-socket2 = { version = "0.5.5", optional = true, features = [ "all" ] }
+socket2 = { version = "0.5.5", optional = true, features = ["all"] }
 
 # Currently unstable. The API exposed by these features may be broken at any time.
 # Requires `--cfg tokio_unstable` to enable.
@@ -123,8 +123,8 @@ optional = true
 [target.'cfg(windows)'.dev-dependencies.windows-sys]
 version = "0.52"
 features = [
-    "Win32_Foundation",
-    "Win32_Security_Authorization",
+  "Win32_Foundation",
+  "Win32_Security_Authorization",
 ]
 
 [dev-dependencies]
@@ -137,6 +137,7 @@ async-stream = "0.3"
 [target.'cfg(not(target_family = "wasm"))'.dev-dependencies]
 socket2 = "0.5.5"
 tempfile = "3.1.0"
+proptest = "1"
 
 [target.'cfg(not(all(target_family = "wasm", target_os = "unknown")))'.dev-dependencies]
 rand = "0.8.0"
@@ -165,8 +166,7 @@ features = ["full", "test-util"]
 # The following are types that are allowed to be exposed in Tokio's public API.
 # The standard library is allowed by default.
 allowed_external_types = [
-   "bytes::buf::buf_impl::Buf",
-   "bytes::buf::buf_mut::BufMut",
-
-   "tokio_macros::*",
+  "bytes::buf::buf_impl::Buf",
+  "bytes::buf::buf_mut::BufMut",
+  "tokio_macros::*",
 ]

tokio/src/runtime/builder.rs

@@ -6,6 +6,8 @@ use crate::runtime::TaskMeta;
 use crate::runtime::{blocking, driver, Callback, HistogramBuilder, Runtime, TaskCallback};
 use crate::util::rand::{RngSeed, RngSeedGenerator};
 
+#[cfg(tokio_unstable)]
+use crate::runtime::metrics::HistogramConfiguration;
 use std::fmt;
 use std::io;
 use std::time::Duration;
@@ -1068,6 +1070,11 @@ impl Builder {
         /// `metrics_poll_count_histogram_` builder methods to configure the
         /// histogram details.
         ///
+        /// By default, a linear histogram with 10 buckets each 100 microseconds wide will be used.
+        /// This has an extremely low memory footprint, but may not provide enough granularity. For
+        /// better granularity with low memory usage, use [`metrics_poll_count_histogram_configuration()`]
+        /// to select [`LogHistogram`] instead.
+        ///
         /// # Examples
         ///
         /// ```
@@ -1087,6 +1094,8 @@ impl Builder {
         ///
         /// [`Handle::metrics()`]: crate::runtime::Handle::metrics
         /// [`Instant::now()`]: std::time::Instant::now
+        /// [`LogHistogram`]: crate::runtime::LogHistogram
+        /// [`metrics_poll_count_histogram_configuration()`]: Builder::metrics_poll_count_histogram_configuration
         pub fn enable_metrics_poll_count_histogram(&mut self) -> &mut Self {
             self.metrics_poll_count_histogram_enable = true;
             self
@@ -1108,14 +1117,58 @@ impl Builder {
         /// ```
         /// use tokio::runtime::{self, HistogramScale};
         ///
+        /// # #[allow(deprecated)]
         /// let rt = runtime::Builder::new_multi_thread()
         ///     .enable_metrics_poll_count_histogram()
         ///     .metrics_poll_count_histogram_scale(HistogramScale::Log)
         ///     .build()
         ///     .unwrap();
         /// ```
+        #[deprecated(note = "use metrics_poll_count_histogram_configuration")]
         pub fn metrics_poll_count_histogram_scale(&mut self, histogram_scale: crate::runtime::HistogramScale) -> &mut Self {
-            self.metrics_poll_count_histogram.scale = histogram_scale;
+            self.metrics_poll_count_histogram.legacy_mut(|b|b.scale = histogram_scale);
+            self
+        }
+
+        /// Configure the histogram for tracking poll times
+        ///
+        /// By default, a linear histogram with 10 buckets each 100 microseconds wide will be used.
+        /// This has an extremely low memory footprint, but may not provide enough granularity. For
+        /// better granularity with low memory usage, use [`LogHistogram`] instead.
+        ///
+        /// # Examples
+        /// Configure a `LogHistogram` with default configuration:
+        /// ```
+        /// use tokio::runtime;
+        /// use tokio::runtime::{HistogramConfiguration, LogHistogram};
+        ///
+        /// let rt = runtime::Builder::new_multi_thread()
+        ///     .enable_metrics_poll_count_histogram()
+        ///     .metrics_poll_count_histogram_configuration(
+        ///         HistogramConfiguration::log(LogHistogram::default())
+        ///     )
+        ///     .build()
+        ///     .unwrap();
+        /// ```
+        ///
+        /// Configure a linear histogram
+        /// ```
+        /// use tokio::runtime;
+        /// use std::time::Duration;
+        /// use tokio::runtime::HistogramConfiguration;
+        ///
+        /// let rt = runtime::Builder::new_multi_thread()
+        ///     .enable_metrics_poll_count_histogram()
+        ///     .metrics_poll_count_histogram_configuration(
+        ///         HistogramConfiguration::linear(Duration::from_micros(10), 100)
+        ///     )
+        ///     .build()
+        ///     .unwrap();
+        /// ```
+        ///
+        /// [`LogHistogram`]: crate::runtime::LogHistogram
+        pub fn metrics_poll_count_histogram_configuration(&mut self, configuration: HistogramConfiguration) -> &mut Self {
+            self.metrics_poll_count_histogram.histogram_type = configuration.inner;
             self
         }
 
@@ -1139,19 +1192,22 @@ impl Builder {
         /// use tokio::runtime;
         /// use std::time::Duration;
         ///
+        /// # #[allow(deprecated)]
         /// let rt = runtime::Builder::new_multi_thread()
         ///     .enable_metrics_poll_count_histogram()
         ///     .metrics_poll_count_histogram_resolution(Duration::from_micros(100))
         ///     .build()
         ///     .unwrap();
         /// ```
+        #[deprecated(note = "use metrics_poll_count_histogram_configuration")]
         pub fn metrics_poll_count_histogram_resolution(&mut self, resolution: Duration) -> &mut Self {
             assert!(resolution > Duration::from_secs(0));
             // Sanity check the argument and also make the cast below safe.
             assert!(resolution <= Duration::from_secs(1));
 
             let resolution = resolution.as_nanos() as u64;
-            self.metrics_poll_count_histogram.resolution = resolution;
+
+            self.metrics_poll_count_histogram.legacy_mut(|b|b.resolution = resolution);
             self
         }
 
@@ -1170,14 +1226,16 @@ impl Builder {
         /// ```
         /// use tokio::runtime;
         ///
+        /// # #[allow(deprecated)]
         /// let rt = runtime::Builder::new_multi_thread()
         ///     .enable_metrics_poll_count_histogram()
         ///     .metrics_poll_count_histogram_buckets(15)
         ///     .build()
         ///     .unwrap();
         /// ```
+        #[deprecated(note = "use `metrics_poll_count_histogram_configuration")]
         pub fn metrics_poll_count_histogram_buckets(&mut self, buckets: usize) -> &mut Self {
-            self.metrics_poll_count_histogram.num_buckets = buckets;
+            self.metrics_poll_count_histogram.legacy_mut(|b|b.num_buckets = buckets);
             self
         }
     }

tokio/src/runtime/metrics/batch.rs

@@ -171,6 +171,6 @@ cfg_rt_multi_thread! {
     }
 }
 
-fn duration_as_u64(dur: Duration) -> u64 {
+pub(crate) fn duration_as_u64(dur: Duration) -> u64 {
     u64::try_from(dur.as_nanos()).unwrap_or(u64::MAX)
 }