[router] enable sccache in ci and local build (#10099)

sgl-router/Makefile

@@ -1,6 +1,15 @@
 # SGLang Router Makefile
 # Provides convenient shortcuts for common development tasks
 
+# Check if sccache is available and set RUSTC_WRAPPER accordingly
+SCCACHE := $(shell which sccache 2>/dev/null)
+ifdef SCCACHE
+    export RUSTC_WRAPPER := $(SCCACHE)
+    $(info Using sccache for compilation caching)
+else
+    $(info sccache not found. Install it for faster builds: cargo install sccache)
+endif
+
 .PHONY: help bench bench-quick bench-baseline bench-compare test build clean
 
 help: ## Show this help message
@@ -90,3 +99,33 @@ perf-monitor: ## Run continuous performance monitoring
 	else \
 		echo "Warning: 'watch' command not found. Install it or run 'make bench-quick' manually."; \
 	fi
+
+# sccache management targets
+setup-sccache: ## Install and configure sccache
+	@echo "Setting up sccache..."
+	@./scripts/setup-sccache.sh
+
+sccache-stats: ## Show sccache statistics
+	@if [ -n "$(SCCACHE)" ]; then \
+		echo "sccache statistics:"; \
+		sccache -s; \
+	else \
+		echo "sccache not installed. Run 'make setup-sccache' to install it."; \
+	fi
+
+sccache-clean: ## Clear sccache cache
+	@if [ -n "$(SCCACHE)" ]; then \
+		echo "Clearing sccache cache..."; \
+		sccache -C; \
+		echo "sccache cache cleared"; \
+	else \
+		echo "sccache not installed"; \
+	fi
+
+sccache-stop: ## Stop the sccache server
+	@if [ -n "$(SCCACHE)" ]; then \
+		echo "Stopping sccache server..."; \
+		sccache --stop-server || true; \
+	else \
+		echo "sccache not installed"; \
+	fi

sgl-router/scripts/setup-sccache.sh

@@ -0,0 +1,84 @@
+#!/usr/bin/env bash
+
+set -Eeuo pipefail
+IFS=$'\n\t'
+
+echo "Setting up sccache for faster Rust compilation..."
+
+has_cmd() { command -v "$1" >/dev/null 2>&1; }
+
+install_sccache() {
+  echo "sccache not found."
+  if [[ "${AUTO_INSTALL:-0}" != "1" ]]; then
+    read -r -p "Install sccache now? [y/N] " response
+    response=${response:-N}
+    if [[ ! "$response" =~ ^[Yy]$ ]]; then
+      echo "Skipping installation. Please install sccache manually:"
+      echo "  cargo install sccache"
+      echo "  or"
+      echo "  brew install sccache (macOS)"
+      echo "  or"
+      echo "  sudo apt-get install -y sccache (Debian/Ubuntu)"
+      echo "  or"
+      echo "  sudo dnf install -y sccache (RHEL/Fedora)"
+      echo "  or"
+      echo "  sudo pacman -S sccache (Arch)"
+      exit 0
+    fi
+  fi
+
+  if has_cmd cargo; then
+    echo "Installing via cargo..."
+    cargo install sccache --locked
+  elif has_cmd brew; then
+    echo "Installing via Homebrew..."
+    brew install sccache
+  elif has_cmd apt-get; then
+    echo "Installing via apt-get..."
+    sudo apt-get update -y && sudo apt-get install -y sccache
+  elif has_cmd dnf; then
+    echo "Installing via dnf..."
+    sudo dnf install -y sccache
+  elif has_cmd pacman; then
+    echo "Installing via pacman..."
+    sudo pacman -S --noconfirm sccache
+  else
+    echo "No supported package manager detected. Install manually:"
+    echo "  cargo install sccache"
+    exit 1
+  fi
+}
+
+if ! has_cmd sccache; then
+  install_sccache
+fi
+
+echo "Configuring sccache..."
+
+export SCCACHE_CACHE_SIZE="${SCCACHE_CACHE_SIZE:-10G}"
+export SCCACHE_STATS="${SCCACHE_STATS:-1}"
+
+# Set RUSTC_WRAPPER to sccache for this shell session.
+SCCACHE_BIN="$(command -v sccache)"
+if [[ -z "${SCCACHE_BIN}" ]]; then
+  echo "Unexpected: sccache still not on PATH after install. Check your environment."
+  exit 1
+fi
+export RUSTC_WRAPPER="${SCCACHE_BIN}"
+
+echo "sccache version: $(sccache --version || echo 'unknown')"
+echo "Current cache stats:"
+sccache -s || true
+
+# If script not sourced, remind user about persistence.
+if [[ "${BASH_SOURCE[0]}" == "$0" ]]; then
+  echo
+  echo "Environment variables exported for this process only."
+  echo "To persist, add to your shell profile (e.g., ~/.bashrc or ~/.zshrc):"
+  echo '  export RUSTC_WRAPPER="$(command -v sccache 2>/dev/null || echo "")"'
+  echo '  export SCCACHE_CACHE_SIZE="10G"'
+  # echo '  export SCCACHE_DIR="$HOME/.cache/sccache"'
+  echo '  export SCCACHE_STATS="1"'
+fi
+
+echo "sccache is configured."

sgl-router/src/core/worker.rs

@@ -986,7 +986,7 @@ pub fn start_health_checker(
 
             // Periodically reset load counters to prevent drift
             // Only do this when we believe all workers should be idle
-            if check_count.is_multiple_of(LOAD_RESET_INTERVAL) {
+            if check_count % LOAD_RESET_INTERVAL == 0 {
                 let max_load = workers_to_check.iter().map(|w| w.load()).max().unwrap_or(0);
                 // Only reset if load appears to be very low (likely drift)
                 if max_load <= 2 {