add program options for tokio histogram settings

Signed-off-by: Jason Volk <jason@zemos.net>

src/main/clap.rs

@@ -38,6 +38,18 @@ pub(crate) struct Args {
 	/// Override the tokio worker_thread count.
 	#[arg(long, hide(true), env = "TOKIO_WORKER_THREADS", default_value = available_parallelism().to_string())]
 	pub(crate) worker_threads: usize,
+
+	/// Set the histogram bucket size, in microseconds (tokio_unstable). Default
+	/// is 25 microseconds. If the values of the histogram don't approach zero
+	/// with the exception of the last bucket, try increasing this value to e.g.
+	/// 50 or 100. Inversely, decrease to 10 etc if the histogram lacks
+	/// resolution.
+	#[arg(long, hide(true), env = "CONDUWUIT_RUNTIME_HISTOGRAM_INTERVAL", default_value = "25")]
+	pub(crate) worker_histogram_interval: u64,
+
+	/// Set the histogram bucket count (tokio_unstable). Default is 20.
+	#[arg(long, hide(true), env = "CONDUWUIT_RUNTIME_HISTOGRAM_BUCKETS", default_value = "20")]
+	pub(crate) worker_histogram_buckets: usize,
 }
 
 /// Parse commandline arguments into structured data

src/main/runtime.rs

@@ -35,25 +35,21 @@ pub(super) fn new(args: &Args) -> Result<tokio::runtime::Runtime> {
 		.on_task_terminate(task_terminate);
 
 	#[cfg(tokio_unstable)]
-	enable_histogram(&mut builder);
+	enable_histogram(&mut builder, args);
 
 	builder.build().map_err(Into::into)
 }
 
 #[cfg(tokio_unstable)]
-fn enable_histogram(builder: &mut Builder) {
+fn enable_histogram(builder: &mut Builder, args: &Args) {
-	use tokio::runtime::{HistogramConfiguration, LogHistogram};
+	use tokio::runtime::HistogramConfiguration;
-
-	let config = LogHistogram::builder()
-		.min_value(Duration::from_micros(10))
-		.max_value(Duration::from_millis(1))
-		.max_error(0.5)
-		.max_buckets(32)
-		.expect("erroneous histogram configuration");
 
+	let buckets = args.worker_histogram_buckets;
+	let interval = Duration::from_micros(args.worker_histogram_interval);
+	let linear = HistogramConfiguration::linear(interval, buckets);
 	builder
 		.enable_metrics_poll_time_histogram()
-		.metrics_poll_time_histogram_configuration(HistogramConfiguration::log(config));
+		.metrics_poll_time_histogram_configuration(linear);
 }
 
 #[tracing::instrument(