From e1355de4cb85ccdcc716e812880dcfcc256a3115 Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@koston.org>
Date: Wed, 28 Jan 2026 06:06:33 -1000
Subject: [PATCH] [runtime_stats] Eliminate heap churn by using stack-allocated
 buffer for sorting (#13586)

---
 .../runtime_stats/runtime_stats.cpp           | 59 ++++++++++++-------
 .../components/runtime_stats/runtime_stats.h  | 12 ----
 2 files changed, 37 insertions(+), 34 deletions(-)

diff --git a/esphome/components/runtime_stats/runtime_stats.cpp b/esphome/components/runtime_stats/runtime_stats.cpp
index 9a1e1a109a..410695da04 100644
--- a/esphome/components/runtime_stats/runtime_stats.cpp
+++ b/esphome/components/runtime_stats/runtime_stats.cpp
@@ -27,46 +27,61 @@ void RuntimeStatsCollector::record_component_time(Component *component, uint32_t
 }
 
 void RuntimeStatsCollector::log_stats_() {
+  // First pass: count active components
+  size_t count = 0;
+  for (const auto &it : this->component_stats_) {
+    if (it.second.get_period_count() > 0) {
+      count++;
+    }
+  }
+
   ESP_LOGI(TAG,
            "Component Runtime Statistics\n"
-           " Period stats (last %" PRIu32 "ms):",
-           this->log_interval_);
+           " Period stats (last %" PRIu32 "ms): %zu active components",
+           this->log_interval_, count);
 
-  // First collect stats we want to display
-  std::vector<ComponentStatPair> stats_to_display;
+  if (count == 0) {
+    return;
+  }
 
+  // Stack buffer sized to actual active count (up to 256 components), heap fallback for larger
+  SmallBufferWithHeapFallback<256, Component *> buffer(count);
+  Component **sorted = buffer.get();
+
+  // Second pass: fill buffer with active components
+  size_t idx = 0;
   for (const auto &it : this->component_stats_) {
-    Component *component = it.first;
-    const ComponentRuntimeStats &stats = it.second;
-    if (stats.get_period_count() > 0) {
-      ComponentStatPair pair = {component, &stats};
-      stats_to_display.push_back(pair);
+    if (it.second.get_period_count() > 0) {
+      sorted[idx++] = it.first;
     }
   }
 
   // Sort by period runtime (descending)
-  std::sort(stats_to_display.begin(), stats_to_display.end(), std::greater<ComponentStatPair>());
+  std::sort(sorted, sorted + count, [this](Component *a, Component *b) {
+    return this->component_stats_[a].get_period_time_ms() > this->component_stats_[b].get_period_time_ms();
+  });
 
   // Log top components by period runtime
-  for (const auto &it : stats_to_display) {
+  for (size_t i = 0; i < count; i++) {
+    const auto &stats = this->component_stats_[sorted[i]];
     ESP_LOGI(TAG, "  %s: count=%" PRIu32 ", avg=%.2fms, max=%" PRIu32 "ms, total=%" PRIu32 "ms",
-             LOG_STR_ARG(it.component->get_component_log_str()), it.stats->get_period_count(),
-             it.stats->get_period_avg_time_ms(), it.stats->get_period_max_time_ms(), it.stats->get_period_time_ms());
+             LOG_STR_ARG(sorted[i]->get_component_log_str()), stats.get_period_count(), stats.get_period_avg_time_ms(),
+             stats.get_period_max_time_ms(), stats.get_period_time_ms());
   }
 
-  // Log total stats since boot
-  ESP_LOGI(TAG, " Total stats (since boot):");
+  // Log total stats since boot (only for active components - idle ones haven't changed)
+  ESP_LOGI(TAG, " Total stats (since boot): %zu active components", count);
 
   // Re-sort by total runtime for all-time stats
-  std::sort(stats_to_display.begin(), stats_to_display.end(),
-            [](const ComponentStatPair &a, const ComponentStatPair &b) {
-              return a.stats->get_total_time_ms() > b.stats->get_total_time_ms();
-            });
+  std::sort(sorted, sorted + count, [this](Component *a, Component *b) {
+    return this->component_stats_[a].get_total_time_ms() > this->component_stats_[b].get_total_time_ms();
+  });
 
-  for (const auto &it : stats_to_display) {
+  for (size_t i = 0; i < count; i++) {
+    const auto &stats = this->component_stats_[sorted[i]];
     ESP_LOGI(TAG, "  %s: count=%" PRIu32 ", avg=%.2fms, max=%" PRIu32 "ms, total=%" PRIu32 "ms",
-             LOG_STR_ARG(it.component->get_component_log_str()), it.stats->get_total_count(),
-             it.stats->get_total_avg_time_ms(), it.stats->get_total_max_time_ms(), it.stats->get_total_time_ms());
+             LOG_STR_ARG(sorted[i]->get_component_log_str()), stats.get_total_count(), stats.get_total_avg_time_ms(),
+             stats.get_total_max_time_ms(), stats.get_total_time_ms());
   }
 }
 
diff --git a/esphome/components/runtime_stats/runtime_stats.h b/esphome/components/runtime_stats/runtime_stats.h
index 56122364c2..c7fea7474b 100644
--- a/esphome/components/runtime_stats/runtime_stats.h
+++ b/esphome/components/runtime_stats/runtime_stats.h
@@ -5,7 +5,6 @@
 #ifdef USE_RUNTIME_STATS
 
 #include <map>
-#include <vector>
 #include <cstdint>
 #include <cstring>
 #include "esphome/core/helpers.h"
@@ -77,17 +76,6 @@ class ComponentRuntimeStats {
   uint32_t total_max_time_ms_;
 };
 
-// For sorting components by run time
-struct ComponentStatPair {
-  Component *component;
-  const ComponentRuntimeStats *stats;
-
-  bool operator>(const ComponentStatPair &other) const {
-    // Sort by period time as that's what we're displaying in the logs
-    return stats->get_period_time_ms() > other.stats->get_period_time_ms();
-  }
-};
-
 class RuntimeStatsCollector {
  public:
   RuntimeStatsCollector();