Reduce logger CPU usage by disabling loop when buffer is empty (#9160)

Co-authored-by: Jesse Hills <3060199+jesserockz@users.noreply.github.com>

esphome/components/logger/logger.cpp

@@ -48,6 +48,11 @@ void HOT Logger::log_vprintf_(uint8_t level, const char *tag, int line, const ch
   // For non-main tasks, queue the message for callbacks - but only if we have any callbacks registered
   message_sent =
       this->log_buffer_->send_message_thread_safe(level, tag, static_cast<uint16_t>(line), current_task, format, args);
+  if (message_sent) {
+    // Enable logger loop to process the buffered message
+    // This is safe to call from any context including ISRs
+    this->enable_loop_soon_any_context();
+  }
 #endif  // USE_ESPHOME_TASK_LOG_BUFFER
 
   // Emergency console logging for non-main tasks when ring buffer is full or disabled
@@ -139,6 +144,10 @@ Logger::Logger(uint32_t baud_rate, size_t tx_buffer_size) : baud_rate_(baud_rate
 #ifdef USE_ESPHOME_TASK_LOG_BUFFER
 void Logger::init_log_buffer(size_t total_buffer_size) {
   this->log_buffer_ = esphome::make_unique<logger::TaskLogBuffer>(total_buffer_size);
+
+  // Start with loop disabled when using task buffer (unless using USB CDC)
+  // The loop will be enabled automatically when messages arrive
+  this->disable_loop_when_buffer_empty_();
 }
 #endif
 
@@ -189,6 +198,10 @@ void Logger::loop() {
         this->write_msg_(this->tx_buffer_);
       }
     }
+  } else {
+    // No messages to process, disable loop if appropriate
+    // This reduces overhead when there's no async logging activity
+    this->disable_loop_when_buffer_empty_();
   }
 #endif
 }

esphome/components/logger/logger.h

@@ -358,6 +358,26 @@ class Logger : public Component {
     static const uint16_t RESET_COLOR_LEN = strlen(ESPHOME_LOG_RESET_COLOR);
     this->write_body_to_buffer_(ESPHOME_LOG_RESET_COLOR, RESET_COLOR_LEN, buffer, buffer_at, buffer_size);
   }
+
+#ifdef USE_ESP32
+  // Disable loop when task buffer is empty (with USB CDC check)
+  inline void disable_loop_when_buffer_empty_() {
+    // Thread safety note: This is safe even if another task calls enable_loop_soon_any_context()
+    // concurrently. If that happens between our check and disable_loop(), the enable request
+    // will be processed on the next main loop iteration since:
+    // - disable_loop() takes effect immediately
+    // - enable_loop_soon_any_context() sets a pending flag that's checked at loop start
+#if defined(USE_LOGGER_USB_CDC) && defined(USE_ARDUINO)
+    // Only disable if not using USB CDC (which needs loop for connection detection)
+    if (this->uart_ != UART_SELECTION_USB_CDC) {
+      this->disable_loop();
+    }
+#else
+    // No USB CDC support, always safe to disable
+    this->disable_loop();
+#endif
+  }
+#endif
 };
 extern Logger *global_logger;  // NOLINT(cppcoreguidelines-avoid-non-const-global-variables)
 

esphome/core/defines.h

@@ -132,6 +132,8 @@
 
 // ESP32-specific feature flags
 #ifdef USE_ESP32
+#define USE_ESPHOME_TASK_LOG_BUFFER
+
 #define USE_BLUETOOTH_PROXY
 #define USE_CAPTIVE_PORTAL
 #define USE_ESP32_BLE