[core/nvnflinger] Rewrite GetBufferHistory (#528)

This rewrite should improve performance with the buffer history by changing the complexity level to O(1).
Replace std::vector with std::array to ensure that elements are allocated on the stack rather than on the free store.
Avoid expensive resizing at runtime.
Adjust buffer states at the right locations.
Tightly pack the BufferHistoryInfo struct to ensure that it only occupies 28 bytes.

Reviewed-on: #528
Co-authored-by: SDK-Chan <sdkchan@eden-emu.dev>
Co-committed-by: SDK-Chan <sdkchan@eden-emu.dev>

src/core/hle/service/nvnflinger/buffer_queue_consumer.cpp

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: Copyright 2025 Eden Emulator Project
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 // SPDX-FileCopyrightText: Copyright 2021 yuzu Emulator Project
 // SPDX-FileCopyrightText: Copyright 2014 The Android Open Source Project
 // SPDX-License-Identifier: GPL-3.0-or-later
@@ -97,18 +100,18 @@ Status BufferQueueConsumer::AcquireBuffer(BufferItem* out_buffer,
         slots[slot].needs_cleanup_on_release = false;
         slots[slot].buffer_state = BufferState::Acquired;
 
+        // Mark tracked buffer history records as acquired
+        for (auto& buffer_history_record : core->buffer_history) {
+            if (buffer_history_record.frame_number == core->frame_counter) {
+                buffer_history_record.state = BufferState::Acquired;
+                break;
+            }
+        }
+
         // TODO: for now, avoid resetting the fence, so that when we next return this
         // slot to the producer, it will wait for the fence to pass. We should fix this
         // by properly waiting for the fence in the BufferItemConsumer.
         // slots[slot].fence = Fence::NoFence();
-
-        const auto target_frame_number = slots[slot].frame_number;
-        for (size_t i = 0; i < core->history.size(); i++) {
-            if (core->history[i].frame_number == target_frame_number) {
-                core->history[i].state = BufferState::Acquired;
-                break;
-            }
-        }
     }
 
     // If the buffer has previously been acquired by the consumer, set graphic_buffer to nullptr to

src/core/hle/service/nvnflinger/buffer_queue_core.cpp

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: Copyright 2025 Eden Emulator Project
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 // SPDX-FileCopyrightText: Copyright 2021 yuzu Emulator Project
 // SPDX-FileCopyrightText: Copyright 2014 The Android Open Source Project
 // SPDX-License-Identifier: GPL-3.0-or-later
@@ -10,12 +13,19 @@
 
 namespace Service::android {
 
-BufferQueueCore::BufferQueueCore() {
+BufferQueueCore::BufferQueueCore() = default;
-    history.resize(8);
-};
-
 BufferQueueCore::~BufferQueueCore() = default;
 
+void BufferQueueCore::PushHistory(u64 frame_number, s64 queue_time, s64 presentation_time, BufferState state) {
+    buffer_history_pos = (buffer_history_pos + 1) % BUFFER_HISTORY_SIZE;
+    buffer_history[buffer_history_pos] = BufferHistoryInfo{
+        .frame_number = frame_number,
+        .queue_time = queue_time,
+        .presentation_time = presentation_time,
+        .state = state,
+    };
+}
+
 void BufferQueueCore::SignalDequeueCondition() {
     dequeue_possible.store(true);
     dequeue_condition.notify_all();
@@ -47,7 +57,7 @@ s32 BufferQueueCore::GetMinMaxBufferCountLocked(bool async) const {
 
 s32 BufferQueueCore::GetMaxBufferCountLocked(bool async) const {
     const auto min_buffer_count = GetMinMaxBufferCountLocked(async);
-    auto max_buffer_count = (std::max)(default_max_buffer_count, min_buffer_count);
+    auto max_buffer_count = std::max(default_max_buffer_count, min_buffer_count);
 
     if (override_max_buffer_count != 0) {
         ASSERT(override_max_buffer_count >= min_buffer_count);

src/core/hle/service/nvnflinger/buffer_queue_core.h

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: Copyright 2025 Eden Emulator Project
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 // SPDX-FileCopyrightText: Copyright 2021 yuzu Emulator Project
 // SPDX-FileCopyrightText: Copyright 2014 The Android Open Source Project
 // SPDX-License-Identifier: GPL-3.0-or-later
@@ -15,6 +18,7 @@
 
 #include "core/hle/service/nvnflinger/buffer_item.h"
 #include "core/hle/service/nvnflinger/buffer_queue_defs.h"
+#include "core/hle/service/nvnflinger/buffer_slot.h"
 #include "core/hle/service/nvnflinger/pixel_format.h"
 #include "core/hle/service/nvnflinger/status.h"
 #include "core/hle/service/nvnflinger/window.h"
@@ -23,22 +27,19 @@ namespace Service::android {
 
 #ifdef _MSC_VER
 #pragma pack(push, 1)
+struct BufferHistoryInfo {
+#elif defined(__GNUC__) || defined(__clang__)
+struct __attribute__((packed)) BufferHistoryInfo {
 #endif
-struct BufferInfo {
     u64 frame_number;
     s64 queue_time;
-    s64 presentation_time{};
+    s64 presentation_time;
-    BufferState state{BufferState::Free};
+    BufferState state;
-}
+};
-#if defined(__GNUC__) || defined(__clang__)
-__attribute__((packed))
-#endif
-;
 #ifdef _MSC_VER
 #pragma pack(pop)
 #endif
-static_assert(sizeof(BufferInfo) == 0x1C,
+static_assert(sizeof(BufferHistoryInfo) == 0x1C, "BufferHistoryInfo must be 28 bytes");
-              "BufferInfo is an invalid size");
 
 class IConsumerListener;
 class IProducerListener;
@@ -49,10 +50,13 @@ class BufferQueueCore final {
 
 public:
     static constexpr s32 INVALID_BUFFER_SLOT = BufferItem::INVALID_BUFFER_SLOT;
+    static constexpr u32 BUFFER_HISTORY_SIZE = 8;
 
     BufferQueueCore();
     ~BufferQueueCore();
 
+    void PushHistory(u64 frame_number, s64 queue_time, s64 presentation_time, BufferState state);
+
 private:
     void SignalDequeueCondition();
     bool WaitForDequeueCondition(std::unique_lock<std::mutex>& lk);
@@ -88,11 +92,11 @@ private:
     const s32 max_acquired_buffer_count{}; // This is always zero on HOS
     bool buffer_has_been_queued{};
     u64 frame_counter{};
+    std::array<BufferHistoryInfo, BUFFER_HISTORY_SIZE> buffer_history{};
+    u32 buffer_history_pos{BUFFER_HISTORY_SIZE-1};
     u32 transform_hint{};
     bool is_allocating{};
     mutable std::condition_variable_any is_allocating_condition;
-
-    std::vector<BufferInfo> history{8};
 };
 
 } // namespace Service::android

src/core/hle/service/nvnflinger/buffer_queue_producer.cpp

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: Copyright 2025 Eden Emulator Project
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 // SPDX-FileCopyrightText: Copyright 2021 yuzu Emulator Project
 // SPDX-FileCopyrightText: Copyright 2014 The Android Open Source Project
 // SPDX-License-Identifier: GPL-3.0-or-later
@@ -530,11 +533,6 @@ Status BufferQueueProducer::QueueBuffer(s32 slot, const QueueBufferInput& input,
         item.is_droppable = core->dequeue_buffer_cannot_block || async;
         item.swap_interval = swap_interval;
 
-        position = (position + 1) % 8;
-        core->history[position] = {.frame_number = core->frame_counter,
-                                   .queue_time = slots[slot].queue_time,
-                                   .state = BufferState::Queued};
-
         sticky_transform = sticky_transform_;
 
         if (core->queue.empty()) {
@@ -551,6 +549,15 @@ Status BufferQueueProducer::QueueBuffer(s32 slot, const QueueBufferInput& input,
                 // mark it as freed
                 if (core->StillTracking(*front)) {
                     slots[front->slot].buffer_state = BufferState::Free;
+
+                    // Mark tracked buffer history records as free
+                    for (auto& buffer_history_record : core->buffer_history) {
+                        if (buffer_history_record.frame_number == front->frame_number) {
+                            buffer_history_record.state = BufferState::Free;
+                            break;
+                        }
+                    }
+
                     // Reset the frame number of the freed buffer so that it is the first in line to
                     // be dequeued again
                     slots[front->slot].frame_number = 0;
@@ -564,6 +571,7 @@ Status BufferQueueProducer::QueueBuffer(s32 slot, const QueueBufferInput& input,
             }
         }
 
+        core->PushHistory(core->frame_counter, slots[slot].queue_time, slots[slot].presentation_time, BufferState::Queued);
         core->buffer_has_been_queued = true;
         core->SignalDequeueCondition();
         output->Inflate(core->default_width, core->default_height, core->transform_hint,
@@ -938,33 +946,46 @@ void BufferQueueProducer::Transact(u32 code, std::span<const u8> parcel_data,
         break;
     }
     case TransactionId::GetBufferHistory: {
-        LOG_WARNING(Service_Nvnflinger, "called, transaction=GetBufferHistory");
+        LOG_DEBUG(Service_Nvnflinger, "called, transaction=GetBufferHistory");
 
-        std::scoped_lock lock{core->mutex};
+        const s32 request = parcel_in.Read<s32>();
-
+        if (request <= 0) {
-        auto buffer_history_count = (std::min)(parcel_in.Read<s32>(), (s32)core->history.size());
-
-        if (buffer_history_count <= 0) {
             parcel_out.Write(Status::BadValue);
             parcel_out.Write<s32>(0);
-            status = Status::None;
             break;
         }
 
-        auto info = new BufferInfo[buffer_history_count];
+        constexpr u32 history_max = BufferQueueCore::BUFFER_HISTORY_SIZE;
-        auto pos = position;
+        std::array<BufferHistoryInfo, history_max> buffer_history_snapshot{};
-        for (int i = 0; i < buffer_history_count; i++) {
+        s32 valid_index{};
-            info[i] = core->history[(pos - i) % core->history.size()];
+        {
-            LOG_WARNING(Service_Nvnflinger, "frame_number={}, state={}",
+            std::scoped_lock lk(core->mutex);
-                        core->history[(pos - i) % core->history.size()].frame_number,
+
-                        (u32)core->history[(pos - i) % core->history.size()].state);
+            const u32 current_history_pos = core->buffer_history_pos;
-            pos--;
+            u32 index_reversed{};
+            for (u32 i = 0; i < history_max; ++i) {
+                // Wrap values backwards e.g. 7, 6, 5, etc. in the range of 0-7
+                index_reversed = (current_history_pos + history_max - i) % history_max;
+                const auto& current_history_buffer = core->buffer_history[index_reversed];
+
+                // Here we use the frame number as a terminator.
+                // Because a buffer without frame_number is not considered complete
+                if (current_history_buffer.frame_number == 0) {
+                    break;
                 }
 
+                buffer_history_snapshot[valid_index] = current_history_buffer;
+                ++valid_index;
+            }
+        }
+
+        const s32 limit = std::min(request, valid_index);
         parcel_out.Write(Status::NoError);
-        parcel_out.Write(buffer_history_count);
+        parcel_out.Write<s32>(limit);
-        parcel_out.WriteFlattenedObject<BufferInfo>(info);
+        for (s32 i = 0; i < limit; ++i) {
-        status = Status::None;
+            parcel_out.Write(buffer_history_snapshot[i]);
+        }
+
         break;
     }
     default:
@@ -972,9 +993,7 @@ void BufferQueueProducer::Transact(u32 code, std::span<const u8> parcel_data,
         break;
     }
 
-    if (status != Status::None) {
     parcel_out.Write(status);
-    }
 
     const auto serialized = parcel_out.Serialize();
     std::memcpy(parcel_reply.data(), serialized.data(),

src/core/hle/service/nvnflinger/buffer_queue_producer.h

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: Copyright 2025 Eden Emulator Project
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 // SPDX-FileCopyrightText: Copyright 2021 yuzu Emulator Project
 // SPDX-FileCopyrightText: Copyright 2014 The Android Open Source Project
 // SPDX-License-Identifier: GPL-3.0-or-later

src/core/hle/service/nvnflinger/buffer_slot.h

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: Copyright 2025 Eden Emulator Project
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 // SPDX-FileCopyrightText: Copyright 2021 yuzu Emulator Project
 // SPDX-FileCopyrightText: Copyright 2014 The Android Open Source Project
 // SPDX-License-Identifier: GPL-3.0-or-later
@@ -15,7 +18,7 @@ namespace Service::android {
 
 class GraphicBuffer;
 
-enum class BufferState : s32 {
+enum class BufferState : u32 {
     Free = 0,
     Dequeued = 1,
     Queued = 2,