[mdns] Throttle MDNS.update() polling on ESP8266 and RP2040 (#13917)

esphome/components/mdns/mdns_component.h

@@ -45,9 +45,28 @@ class MDNSComponent : public Component {
   void setup() override;
   void dump_config() override;
 
-#if (defined(USE_ESP8266) || defined(USE_RP2040)) && defined(USE_ARDUINO)
-  void loop() override;
-#endif
+  // Polling interval for MDNS.update() on platforms that require it (ESP8266, RP2040).
+  //
+  // On these platforms, MDNS.update() calls _process(true) which only manages timer-driven
+  // state machines (probe/announce timeouts and service query cache TTLs). Incoming mDNS
+  // packets are handled independently via the lwIP onRx UDP callback and are NOT affected
+  // by how often update() is called.
+  //
+  // The shortest internal timer is the 250ms probe interval (RFC 6762 Section 8.1).
+  // Announcement intervals are 1000ms and cache TTL checks are on the order of seconds
+  // to minutes. A 50ms polling interval provides sufficient resolution for all timers
+  // while completely removing mDNS from the per-iteration loop list.
+  //
+  // In steady state (after the ~8 second boot probe/announce phase completes), update()
+  // checks timers that are set to never expire, making every call pure overhead.
+  //
+  // Tasmota uses a 50ms main loop cycle with mDNS working correctly, confirming this
+  // interval is safe in production.
+  //
+  // By using set_interval() instead of overriding loop(), the component is excluded from
+  // the main loop list via has_overridden_loop(), eliminating all per-iteration overhead
+  // including virtual dispatch.
+  static constexpr uint32_t MDNS_UPDATE_INTERVAL_MS = 50;
   float get_setup_priority() const override { return setup_priority::AFTER_CONNECTION; }
 
 #ifdef USE_MDNS_EXTRA_SERVICES

esphome/components/mdns/mdns_esp8266.cpp

@@ -36,9 +36,14 @@ static void register_esp8266(MDNSComponent *, StaticVector<MDNSService, MDNS_SER
   }
 }
 
-void MDNSComponent::setup() { this->setup_buffers_and_register_(register_esp8266); }
-
-void MDNSComponent::loop() { MDNS.update(); }
+void MDNSComponent::setup() {
+  this->setup_buffers_and_register_(register_esp8266);
+  // Schedule MDNS.update() via set_interval() instead of overriding loop().
+  // This removes the component from the per-iteration loop list entirely,
+  // eliminating virtual dispatch overhead on every main loop cycle.
+  // See MDNS_UPDATE_INTERVAL_MS comment in mdns_component.h for safety analysis.
+  this->set_interval(MDNS_UPDATE_INTERVAL_MS, []() { MDNS.update(); });
+}
 
 void MDNSComponent::on_shutdown() {
   MDNS.close();

esphome/components/mdns/mdns_rp2040.cpp

@@ -35,9 +35,14 @@ static void register_rp2040(MDNSComponent *, StaticVector<MDNSService, MDNS_SERV
   }
 }
 
-void MDNSComponent::setup() { this->setup_buffers_and_register_(register_rp2040); }
-
-void MDNSComponent::loop() { MDNS.update(); }
+void MDNSComponent::setup() {
+  this->setup_buffers_and_register_(register_rp2040);
+  // Schedule MDNS.update() via set_interval() instead of overriding loop().
+  // This removes the component from the per-iteration loop list entirely,
+  // eliminating virtual dispatch overhead on every main loop cycle.
+  // See MDNS_UPDATE_INTERVAL_MS comment in mdns_component.h for safety analysis.
+  this->set_interval(MDNS_UPDATE_INTERVAL_MS, []() { MDNS.update(); });
+}
 
 void MDNSComponent::on_shutdown() {
   MDNS.close();