[wifi] Skip xQueueReceive when no WiFi events pending on ESP-IDF

Add an atomic counter incremented when events are enqueued and
decremented when dequeued. wifi_loop_() checks this counter before
calling xQueueReceive, avoiding the FreeRTOS kernel call on every
loop iteration when no events are pending (the common case).

This matches the fast-path pattern used by the scheduler to avoid
lock overhead when there is nothing to process.

esphome/components/wifi/wifi_component_esp_idf.cpp

@@ -13,6 +13,7 @@
 #include <freertos/task.h>
 
 #include <algorithm>
+#include <atomic>
 #include <cinttypes>
 #include <memory>
 #include <utility>
@@ -48,7 +49,10 @@ static const char *const TAG = "wifi_esp32";
 
 static EventGroupHandle_t s_wifi_event_group;  // NOLINT(cppcoreguidelines-avoid-non-const-global-variables)
 static QueueHandle_t s_event_queue;            // NOLINT(cppcoreguidelines-avoid-non-const-global-variables)
-static esp_netif_t *s_sta_netif = nullptr;     // NOLINT(cppcoreguidelines-avoid-non-const-global-variables)
+// Fast-path counter to skip xQueueReceive kernel call when queue is empty.
+// Incremented from event handler (ISR-safe context), read from main loop.
+static std::atomic<uint32_t> s_event_count{0};  // NOLINT(cppcoreguidelines-avoid-non-const-global-variables)
+static esp_netif_t *s_sta_netif = nullptr;      // NOLINT(cppcoreguidelines-avoid-non-const-global-variables)
 #ifdef USE_WIFI_AP
 static esp_netif_t *s_ap_netif = nullptr;     // NOLINT(cppcoreguidelines-avoid-non-const-global-variables)
 #endif                                        // USE_WIFI_AP
@@ -138,6 +142,8 @@ void event_handler(void *arg, esp_event_base_t event_base, int32_t event_id, voi
   // don't block, we may miss events but the core can handle that
   if (xQueueSend(s_event_queue, &to_send, 0L) != pdPASS) {
     delete to_send;  // NOLINT(cppcoreguidelines-owning-memory)
+  } else {
+    s_event_count.fetch_add(1, std::memory_order_release);
   }
 }
 
@@ -724,12 +730,18 @@ const char *get_disconnect_reason_str(uint8_t reason) {
 }
 
 void WiFiComponent::wifi_loop_() {
+  // Fast path: skip xQueueReceive kernel call when no events are pending.
+  // The atomic load is much cheaper than entering the FreeRTOS kernel.
+  if (s_event_count.load(std::memory_order_acquire) == 0)
+    return;
+
   while (true) {
     IDFWiFiEvent *data;
     if (xQueueReceive(s_event_queue, &data, 0L) != pdTRUE) {
       // no event ready
       break;
     }
+    s_event_count.fetch_sub(1, std::memory_order_relaxed);
 
     // process event
     wifi_process_event_(data);