Histogram support in runtime metrics (#6935)

* Histogram support in runtime metrics

Add support for histograms to the runtime metrics. Additionally add
`polkadot_parachain_verify_dispute_signature` histogram which tracks the
time needed from the runtime to verify a single validator signature of a
dispute statement.

* Add noops

* u64 instead of f64

* Update buckets

* Wrap `get_current_time()` in runtime metrics

* Change the dimension of the Histogram from usec to sec

* Fix a compilation error

* Update buckets

* Fix `on_signature_check_complete` calculation

* Update buckets

* Update buckets

* formatting

* Another weights update

* Adjust buckets again

* Final buckets adjustment

* Revert "Fix a compilation error"

This reverts commit 06290b40a39eeb78de2602d8916a39edf7a8b714.

* Update primitives/src/v4/metrics.rs

Co-authored-by: Andrei Sandu <54316454+sandreim@users.noreply.github.com>

* Use `saturating_sub` for time difference calculation

* Pass nanoseconds to client instead of seconds (using f64 in runtime is dangerous)

---------

Co-authored-by: Andrei Sandu <54316454+sandreim@users.noreply.github.com>

polkadot/runtime/metrics/src/with_runtime_metrics.rs

@@ -14,17 +14,17 @@
 // You should have received a copy of the GNU General Public License
 // along with Polkadot.  If not, see <http://www.gnu.org/licenses/>.
 
-//! This module provides an implementation for the runtime metrics types: `Counter`
-//! and `CounterVec`. These types expose a Prometheus like interface and same functionality.
-//! Each instance of a runtime metric is mapped to a Prometheus metric on the client side.
-//! The runtime metrics must be registered with the registry in the client, otherwise
-//! they will not be published.
+//! This module provides an implementation for the runtime metrics types: `Counter`,
+//! `CounterVec` and `Histogram`. These types expose a Prometheus like interface and
+//! same functionality. Each instance of a runtime metric is mapped to a Prometheus
+//! metric on the client side. The runtime metrics must be registered with the registry
+//! in the client, otherwise they will not be published.
 
 const TRACING_TARGET: &'static str = "metrics";
 
 use parity_scale_codec::Encode;
 use primitives::{
-	metric_definitions::{CounterDefinition, CounterVecDefinition},
+	metric_definitions::{CounterDefinition, CounterVecDefinition, HistogramDefinition},
 	RuntimeMetricLabelValues, RuntimeMetricOp, RuntimeMetricUpdate,
 };
 
@@ -41,6 +41,10 @@ pub struct Counter {
 	name: &'static str,
 }
 
+pub struct Histogram {
+	name: &'static str,
+}
+
 /// Convenience trait implemented for all metric types.
 trait MetricEmitter {
 	fn emit(metric_op: &RuntimeMetricUpdate) {
@@ -77,6 +81,7 @@ impl LabeledMetric {
 
 impl MetricEmitter for LabeledMetric {}
 impl MetricEmitter for Counter {}
+impl MetricEmitter for Histogram {}
 
 impl CounterVec {
 	/// Create a new counter as specified by `definition`. This metric needs to be registered
@@ -116,3 +121,27 @@ impl Counter {
 		self.inc_by(1);
 	}
 }
+
+impl Histogram {
+	/// Create a new histogram as specified by `definition`. This metric needs to be registered
+	/// in the client before it can be used.
+	pub const fn new(definition: HistogramDefinition) -> Self {
+		// No register op is emitted since the metric is supposed to be registered
+		// on the client by the time `inc()` is called.
+		Histogram { name: definition.name }
+	}
+
+	// Observe a value in the histogram
+	pub fn observe(&self, value: u128) {
+		let metric_update = RuntimeMetricUpdate {
+			metric_name: Vec::from(self.name),
+			op: RuntimeMetricOp::ObserveHistogram(value),
+		};
+		Self::emit(&metric_update);
+	}
+}
+
+/// Returns current time in ns
+pub fn get_current_time() -> u128 {
+	frame_benchmarking::benchmarking::current_time()
+}

polkadot/runtime/metrics/src/without_runtime_metrics.rs

@@ -18,13 +18,18 @@
 //! provide a dummy implementation for the native runtime to avoid cluttering the runtime code
 //! with `#[cfg(feature = "runtime-metrics")]`.
 
-use primitives::metric_definitions::{CounterDefinition, CounterVecDefinition};
+use primitives::metric_definitions::{
+	CounterDefinition, CounterVecDefinition, HistogramDefinition,
+};
 
 /// A dummy `Counter`.
 pub struct Counter;
 /// A dummy `CounterVec`.
 pub struct CounterVec;
 
+/// A dummy `Histogram`
+pub struct Histogram;
+
 /// Dummy implementation.
 impl CounterVec {
 	/// Constructor.
@@ -52,3 +57,20 @@ impl Counter {
 	/// Increment counter, implementation is a `no op`.
 	pub fn inc(&self) {}
 }
+
+/// Dummy implementation
+impl Histogram {
+	/// Create a new histogram as specified by `definition`. This metric needs to be registered
+	/// in the client before it can be used.
+	pub const fn new(_definition: HistogramDefinition) -> Self {
+		Histogram
+	}
+
+	// Observe a value in the histogram
+	pub fn observe(&self, _value: u128) {}
+}
+
+/// Dummy implementation - always 0
+pub fn get_current_time() -> u128 {
+	0
+}