Reduce default TimeoutLoadReduction , use a quartic curve

Author: jedisct1

dnscrypt-proxy/config.go

@@ -148,7 +148,7 @@ func newConfig() Config {
 		SourceDoH:                true,
 		SourceODoH:               false,
 		MaxClients:               250,
-		TimeoutLoadReduction:     0.5,
+		TimeoutLoadReduction:     0.4,
 		BootstrapResolvers:       []string{DefaultBootstrapResolver},
 		IgnoreSystemDNS:          false,
 		LogMaxSize:               10,

dnscrypt-proxy/config_loader.go

@@ -173,8 +173,8 @@ func configureServerParams(proxy *Proxy, config *Config) {
 	proxy.maxClients = config.MaxClients
 	proxy.timeoutLoadReduction = config.TimeoutLoadReduction
 	if proxy.timeoutLoadReduction < 0.0 || proxy.timeoutLoadReduction > 1.0 {
-		dlog.Warnf("timeout_load_reduction must be between 0.0 and 1.0, using default 0.5")
-		proxy.timeoutLoadReduction = 0.5
+		dlog.Warnf("timeout_load_reduction must be between 0.0 and 1.0, using default 0.4")
+		proxy.timeoutLoadReduction = 0.4
 	}
 	proxy.mainProto = "udp"
 	if config.ForceTCP {

dnscrypt-proxy/example-dnscrypt-proxy.toml

@@ -196,13 +196,15 @@ keepalive = 30
 ## Dynamically reduce query timeout as the number of concurrent connections
 ## approaches max_clients to prevent overload. Value must be between 0.0 and 1.0.
 ## 0.0 = no reduction, 1.0 = maximum reduction.
-## For example, with timeout=5000ms, max_clients=250, and timeout_load_reduction=0.5:
-## - At 125 connections (50% load): timeout remains ~5000ms
-## - At 187 connections (75% load): timeout reduces to ~3750ms
-## - At 225 connections (90% load): timeout reduces to ~2500ms
+## Uses a quartic curve to keep timeout high at low load and reduce sharply near limit.
+## For example, with timeout=5000ms, max_clients=250, and timeout_load_reduction=0.4:
+## - At 125 connections (50% load): timeout remains ~4875ms (97.5%)
+## - At 187 connections (75% load): timeout reduces to ~4373ms (87.5%)
+## - At 225 connections (90% load): timeout reduces to ~3687ms (73.7%)
+## - At 250 connections (100% load): timeout reduces to ~3000ms (60%)
 ## This helps maintain responsiveness under high load by failing fast.
 
-# timeout_load_reduction = 0.5
+# timeout_load_reduction = 0.4
 
 ## Set to `true` to enable hot reloading of configuration files (like allowed-names.txt,
 ## blocked-names.txt, etc.) when they are modified. This can increase CPU and memory usage.

dnscrypt-proxy/proxy.go

@@ -696,7 +696,9 @@ func (proxy *Proxy) getDynamicTimeout() time.Duration {
 	currentClients := atomic.LoadUint32(&proxy.clientsCount)
 	utilization := float64(currentClients) / float64(proxy.maxClients)
 
-	factor := 1.0 - (utilization * utilization * proxy.timeoutLoadReduction)
+	// Use quartic (power 4) curve for slow decrease at low load, sharp decrease near limit
+	utilization4 := utilization * utilization * utilization * utilization
+	factor := 1.0 - (utilization4 * proxy.timeoutLoadReduction)
 	if factor < 0.1 {
 		factor = 0.1
 	}