[benchmark] Add sensor publish_state benchmarks (#15034)

tests/benchmarks/components/sensor/bench_sensor_publish.cpp

@@ -0,0 +1,79 @@
+#include <benchmark/benchmark.h>
+
+#include "esphome/components/sensor/sensor.h"
+
+namespace esphome::benchmarks {
+
+// Inner iteration count to amortize CodSpeed instrumentation overhead.
+// Without this, the ~60ns per-iteration valgrind start/stop cost dominates
+// sub-microsecond benchmarks.
+static constexpr int kInnerIterations = 2000;
+
+// Test subclass to access protected configure_entity_() for benchmark setup.
+class TestSensor : public sensor::Sensor {
+ public:
+  void configure(const char *name) { this->configure_entity_(name, 0x12345678, 0); }
+};
+
+// --- Sensor::publish_state() with no callbacks registered ---
+// Measures baseline publish overhead: state assignment, logging,
+// internal_send_state_to_frontend, ControllerRegistry notification.
+
+static void SensorPublish_NoCallbacks(benchmark::State &state) {
+  TestSensor sensor;
+  sensor.configure("test_sensor");
+
+  for (auto _ : state) {
+    for (int i = 0; i < kInnerIterations; i++) {
+      sensor.publish_state(static_cast<float>(i));
+    }
+    benchmark::DoNotOptimize(sensor.state);
+  }
+  state.SetItemsProcessed(state.iterations() * kInnerIterations);
+}
+BENCHMARK(SensorPublish_NoCallbacks);
+
+// --- Sensor::publish_state() with one state callback ---
+// Measures callback dispatch overhead through LazyCallbackManager.
+
+static void SensorPublish_WithCallback(benchmark::State &state) {
+  TestSensor sensor;
+  sensor.configure("test_sensor");
+
+  float callback_value = 0.0f;
+  sensor.add_on_state_callback([&callback_value](float value) { callback_value = value; });
+
+  for (auto _ : state) {
+    for (int i = 0; i < kInnerIterations; i++) {
+      sensor.publish_state(static_cast<float>(i));
+    }
+    benchmark::DoNotOptimize(callback_value);
+  }
+  state.SetItemsProcessed(state.iterations() * kInnerIterations);
+}
+BENCHMARK(SensorPublish_WithCallback);
+
+// --- Sensor::publish_state() with the same value every time ---
+// Steady-state pattern: sensor reports an unchanged reading.
+// Sensor doesn't dedup today, so this exercises the same code path
+// as changing values, but tracks the common real-world pattern
+// separately for regression detection.
+
+static void SensorPublish_SameValue(benchmark::State &state) {
+  TestSensor sensor;
+  sensor.configure("test_sensor");
+
+  // Warm up so has_state is already set
+  sensor.publish_state(23.5f);
+
+  for (auto _ : state) {
+    for (int i = 0; i < kInnerIterations; i++) {
+      sensor.publish_state(23.5f);
+    }
+    benchmark::DoNotOptimize(sensor.state);
+  }
+  state.SetItemsProcessed(state.iterations() * kInnerIterations);
+}
+BENCHMARK(SensorPublish_SameValue);
+
+}  // namespace esphome::benchmarks