make sender workers default better and clamp value to core count

src/core/config/mod.rs

@@ -1828,7 +1828,7 @@ pub struct Config {
 	/// setting a non-zero value.
 	///
 	/// default: 0
-	#[serde(default)]
+	#[serde(default = "default_sender_workers")]
 	pub sender_workers: usize,
 
 	/// Enables listener sockets; can be set to false to disable listening. This
@@ -2315,6 +2315,8 @@ fn default_stream_width_scale() -> f32 { 1.0 }
 
 fn default_stream_amplification() -> usize { 1024 }
 
+fn default_sender_workers() -> usize { 4 }
+
 fn default_client_receive_timeout() -> u64 { 75 }
 
 fn default_client_request_timeout() -> u64 { 180 }

src/service/sending/mod.rs

@@ -401,16 +401,10 @@ impl Service {
 
 fn num_senders(args: &crate::Args<'_>) -> usize {
 	const MIN_SENDERS: usize = 1;
-	// Limit the number of senders to the number of workers threads or number of
-	// cores, conservatively.
-	let max_senders = args
-		.server
-		.metrics
-		.num_workers()
-		.min(available_parallelism());
+	// Limit the maximum number of senders to the number of cores.
+	let max_senders = available_parallelism();
 
-	// If the user doesn't override the default 0, this is intended to then default
-	// to 1 for now as multiple senders is experimental.
+	// default is 4 senders. clamp between 1 and core count.
 	args.server
 		.config
 		.sender_workers