add tracing_flame_filter config option

The previous hardcoded filter `trace,h2=off` isn't appropriate in all
cases, it's better to have this be configurable.

src/config/mod.rs

@@ -175,6 +175,9 @@ pub(crate) struct Config {
 	#[serde(default)]
 	#[cfg(feature = "perf_measurements")]
 	pub(crate) tracing_flame: bool,
+	#[serde(default = "default_tracing_flame_filter")]
+	#[cfg(feature = "perf_measurements")]
+	pub(crate) tracing_flame_filter: String,
 	#[serde(default)]
 	pub(crate) proxy: ProxyConfig,
 	pub(crate) jwt_secret: Option<String>,
@@ -934,6 +937,9 @@ fn default_pusher_idle_timeout() -> u64 { 15 }
 
 fn default_max_fetch_prev_events() -> u16 { 100_u16 }
 
+#[cfg(feature = "perf_measurements")]
+fn default_tracing_flame_filter() -> String { "trace,h2=off".to_owned() }
+
 fn default_trusted_servers() -> Vec<OwnedServerName> { vec![OwnedServerName::try_from("matrix.org").unwrap()] }
 
 fn default_log() -> String {

src/main.rs

@@ -617,7 +617,10 @@ fn init_tracing(config: &Config) -> LogLevelReloadHandles {
 	#[cfg(feature = "perf_measurements")]
 	let subscriber = {
 		let flame_layer = if config.tracing_flame {
-			let flame_filter = EnvFilter::new("trace,h2=off");
+			let flame_filter = match EnvFilter::try_new(&config.tracing_flame_filter) {
+				Ok(flame_filter) => flame_filter,
+				Err(e) => panic!("tracing_flame_filter config value is invalid: {e}"),
+			};
 
 			// TODO: actually preserve this guard until exit: https://docs.rs/tracing-flame/latest/tracing_flame/struct.FlameLayer.html#dropping-and-flushing
 			let (flame_layer, _guard) = tracing_flame::FlameLayer::with_file("./tracing.folded").unwrap();