[core] Inline feed_wdt hot path with out-of-line slow path (#15656)

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

esphome/core/application.cpp

@@ -209,21 +209,27 @@ void Application::process_dump_config_() {
   this->dump_config_at_++;
 }
 
-void HOT Application::feed_wdt(uint32_t time) {
-  static uint32_t last_feed = 0;
-  // Use provided time if available, otherwise get current time
-  uint32_t now = time ? time : millis();
-  // Compare in milliseconds (3ms threshold)
-  if (now - last_feed > 3) {
-    arch_feed_wdt();
-    last_feed = now;
-#ifdef USE_STATUS_LED
-    if (status_led::global_status_led != nullptr) {
-      status_led::global_status_led->call();
-    }
-#endif
+void Application::feed_wdt() {
+  // Cold entry: callers without a millis() timestamp in hand. Fetches the
+  // time and takes the same rate-limit path as feed_wdt_with_time().
+  uint32_t now = millis();
+  if (now - this->last_wdt_feed_ > WDT_FEED_INTERVAL_MS) {
+    this->feed_wdt_slow_(now);
   }
 }
+
+void HOT Application::feed_wdt_slow_(uint32_t time) {
+  // Callers (both feed_wdt() and feed_wdt_with_time()) have already
+  // confirmed the WDT_FEED_INTERVAL_MS rate limit was exceeded.
+  arch_feed_wdt();
+  this->last_wdt_feed_ = time;
+#ifdef USE_STATUS_LED
+  if (status_led::global_status_led != nullptr) {
+    status_led::global_status_led->call();
+  }
+#endif
+}
+
 bool Application::any_component_has_status_flag_(uint8_t flag) const {
   // Walk all components (not just looping ones) so non-looping components'
   // status bits are respected. Only called from the slow-path clear helpers
@@ -325,7 +331,7 @@ void Application::teardown_components(uint32_t timeout_ms) {
 
   while (pending_count > 0 && (now - start_time) < timeout_ms) {
     // Feed watchdog during teardown to prevent triggering
-    this->feed_wdt(now);
+    this->feed_wdt_with_time(now);
 
     // Process components and compact the array, keeping only those still pending
     size_t still_pending = 0;

esphome/core/application.h

@@ -385,7 +385,24 @@ class Application {
 
   void schedule_dump_config() { this->dump_config_at_ = 0; }
 
-  void feed_wdt(uint32_t time = 0);
+  /// Minimum interval between real arch_feed_wdt() calls. Chosen to keep the
+  /// rate of HAL pokes low while still being small enough that any plausible
+  /// watchdog timeout (seconds) has orders of magnitude of safety margin.
+  static constexpr uint32_t WDT_FEED_INTERVAL_MS = 3;
+
+  /// Feed the task watchdog. Cold entry — callers without a millis()
+  /// timestamp in hand. Out of line to keep call sites tiny.
+  void feed_wdt();
+
+  /// Feed the task watchdog, hot entry. Callers that already have a
+  /// millis() timestamp pay only a load + sub + branch on the common
+  /// (no-op) path. The actual arch feed + status LED update live in
+  /// feed_wdt_slow_.
+  void ESPHOME_ALWAYS_INLINE feed_wdt_with_time(uint32_t time) {
+    if (static_cast<uint32_t>(time - this->last_wdt_feed_) > WDT_FEED_INTERVAL_MS) [[unlikely]] {
+      this->feed_wdt_slow_(time);
+    }
+  }
 
   void reboot();
 
@@ -632,7 +649,10 @@ class Application {
   /// Caller must ensure dump_config_at_ < components_.size().
   void __attribute__((noinline)) process_dump_config_();
 
-  void feed_wdt_arch_();
+  /// Slow path for feed_wdt(): actually calls arch_feed_wdt(), updates
+  /// last_wdt_feed_, and re-dispatches the status LED. Out of line so the
+  /// inline wrapper stays tiny.
+  void feed_wdt_slow_(uint32_t time);
 
   /// Perform a delay while also monitoring socket file descriptors for readiness
 #ifdef USE_HOST
@@ -686,6 +706,7 @@ class Application {
   // 4-byte members
   uint32_t last_loop_{0};
   uint32_t loop_component_start_time_{0};
+  uint32_t last_wdt_feed_{0};  // millis() of most recent arch_feed_wdt(); rate-limits feed_wdt() hot path
 
 #ifdef USE_HOST
   int max_fd_{-1};  // Highest file descriptor number for select()
@@ -830,12 +851,13 @@ inline void ESPHOME_ALWAYS_INLINE Application::before_loop_tasks_(uint32_t loop_
   this->drain_wake_notifications_();
 #endif
 
-  // Process scheduled tasks
+  // Process scheduled tasks. Scheduler::call now feeds the watchdog itself
+  // after each scheduled item that actually runs, so we no longer need an
+  // unconditional feed here — when Scheduler::call has no work to do, the
+  // only elapsed time is a sleep wake + a few instructions, and when it does
+  // have work, it fed the wdt as it went.
   this->scheduler.call(loop_start_time);
 
-  // Feed the watchdog timer
-  this->feed_wdt(loop_start_time);
-
   // Process any pending enable_loop requests from ISRs
   // This must be done before marking in_loop_ = true to avoid race conditions
   if (this->has_pending_enable_loop_requests_) {
@@ -874,7 +896,7 @@ inline void ESPHOME_ALWAYS_INLINE Application::loop() {
       // Use the finish method to get the current time as the end time
       last_op_end_time = guard.finish();
     }
-    this->feed_wdt(last_op_end_time);
+    this->feed_wdt_with_time(last_op_end_time);
   }
 
   this->after_loop_tasks_();

esphome/core/scheduler.cpp

@@ -739,7 +739,13 @@ uint32_t HOT Scheduler::execute_item_(SchedulerItem *item, uint32_t now) {
   App.set_current_component(item->component);
   WarnIfComponentBlockingGuard guard{item->component, now};
   item->callback();
-  return guard.finish();
+  uint32_t end = guard.finish();
+  // Feed the watchdog after each scheduled item (both main heap and defer
+  // queue paths go through here). A run of back-to-back callbacks cannot
+  // starve the wdt. The inline fast path is a load + sub + branch — nearly
+  // free when the 3 ms rate limit hasn't elapsed.
+  App.feed_wdt_with_time(end);
+  return end;
 }
 
 // Common implementation for cancel operations - handles locking