From 248dfb2334d20a2773730b21161c402455a24eae Mon Sep 17 00:00:00 2001
From: Jonah Williams <jonahwilliams@google.com>
Date: Wed, 21 Aug 2024 09:31:55 -0700
Subject: [PATCH] [engine] reland weaken affinity of raster/ui to non-e core
 instead of only fast core (flutter/engine#54616)

Some android devices have only a single fast core. We set the threading affinity for UI/Raster to the fast core, which can lead to the UI/Raster being serialized on this thread. Instead, we should weaken /invert the affinity to "Not slow cores".

FIxes https://github.com/flutter/flutter/issues/153690

Customer money will see some benchmark regressions but they can deal.
---
 engine/src/flutter/fml/cpu_affinity.cc                        | 4 ++++
 engine/src/flutter/fml/cpu_affinity.h                         | 4 ++++
 engine/src/flutter/fml/cpu_affinity_unittests.cc              | 3 +++
 .../flutter/shell/platform/android/android_shell_holder.cc    | 4 ++--
 4 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/engine/src/flutter/fml/cpu_affinity.cc b/engine/src/flutter/fml/cpu_affinity.cc
index ccb2e89686..0342c85f04 100644
--- a/engine/src/flutter/fml/cpu_affinity.cc
+++ b/engine/src/flutter/fml/cpu_affinity.cc
@@ -58,6 +58,8 @@ CPUSpeedTracker::CPUSpeedTracker(std::vector<CpuIndexAndSpeed> data)
     }
     if (data.speed == min_speed_value) {
       efficiency_.push_back(data.index);
+    } else {
+      not_efficiency_.push_back(data.index);
     }
   }
 
@@ -77,6 +79,8 @@ const std::vector<size_t>& CPUSpeedTracker::GetIndices(
       return efficiency_;
     case CpuAffinity::kNotPerformance:
       return not_performance_;
+    case CpuAffinity::kNotEfficiency:
+      return not_efficiency_;
   }
 }
 
diff --git a/engine/src/flutter/fml/cpu_affinity.h b/engine/src/flutter/fml/cpu_affinity.h
index b4c54c7bbf..c1d8498e65 100644
--- a/engine/src/flutter/fml/cpu_affinity.h
+++ b/engine/src/flutter/fml/cpu_affinity.h
@@ -26,6 +26,9 @@ enum class CpuAffinity {
 
   /// @brief Request affinity for all non-performance cores.
   kNotPerformance,
+
+  /// @brief Request affinity for all non-efficiency cores.
+  kNotEfficiency,
 };
 
 /// @brief Request count of efficiency cores.
@@ -79,6 +82,7 @@ class CPUSpeedTracker {
   std::vector<size_t> efficiency_;
   std::vector<size_t> performance_;
   std::vector<size_t> not_performance_;
+  std::vector<size_t> not_efficiency_;
 };
 
 /// @note Visible for testing.
diff --git a/engine/src/flutter/fml/cpu_affinity_unittests.cc b/engine/src/flutter/fml/cpu_affinity_unittests.cc
index 8a5c90687e..142fc84612 100644
--- a/engine/src/flutter/fml/cpu_affinity_unittests.cc
+++ b/engine/src/flutter/fml/cpu_affinity_unittests.cc
@@ -29,6 +29,9 @@ TEST(CpuAffinity, NormalSlowMedFastCores) {
   ASSERT_EQ(tracker.GetIndices(CpuAffinity::kNotPerformance).size(), 2u);
   ASSERT_EQ(tracker.GetIndices(CpuAffinity::kNotPerformance)[0], 0u);
   ASSERT_EQ(tracker.GetIndices(CpuAffinity::kNotPerformance)[1], 1u);
+  ASSERT_EQ(tracker.GetIndices(CpuAffinity::kNotEfficiency).size(), 2u);
+  ASSERT_EQ(tracker.GetIndices(CpuAffinity::kNotEfficiency)[0], 1u);
+  ASSERT_EQ(tracker.GetIndices(CpuAffinity::kNotEfficiency)[1], 2u);
 }
 
 TEST(CpuAffinity, NoCpuData) {
diff --git a/engine/src/flutter/shell/platform/android/android_shell_holder.cc b/engine/src/flutter/shell/platform/android/android_shell_holder.cc
index 74d37e5958..4312ee9f33 100644
--- a/engine/src/flutter/shell/platform/android/android_shell_holder.cc
+++ b/engine/src/flutter/shell/platform/android/android_shell_holder.cc
@@ -49,14 +49,14 @@ static void AndroidPlatformThreadConfigSetter(
       break;
     }
     case fml::Thread::ThreadPriority::kDisplay: {
-      fml::RequestAffinity(fml::CpuAffinity::kPerformance);
+      fml::RequestAffinity(fml::CpuAffinity::kNotEfficiency);
       if (::setpriority(PRIO_PROCESS, 0, -1) != 0) {
         FML_LOG(ERROR) << "Failed to set UI task runner priority";
       }
       break;
     }
     case fml::Thread::ThreadPriority::kRaster: {
-      fml::RequestAffinity(fml::CpuAffinity::kPerformance);
+      fml::RequestAffinity(fml::CpuAffinity::kNotEfficiency);
       // Android describes -8 as "most important display threads, for
       // compositing the screen and retrieving input events". Conservatively
       // set the raster thread to slightly lower priority than it.