From 447f29285fbf9d148c7cbccdf0f6fb08bbe566e8 Mon Sep 17 00:00:00 2001
From: GPUCode <geoster3d@gmail.com>
Date: Sun, 8 Jan 2023 15:04:28 +0200
Subject: [PATCH] renderer_vulkan: Add fence implementation of MasterSemaphore

---
 .../renderer_vulkan/vk_master_semaphore.cpp   |  17 +++
 .../renderer_vulkan/vk_master_semaphore.h     | 125 ++++++++++++++++++
 2 files changed, 142 insertions(+)

diff --git a/src/video_core/renderer_vulkan/vk_master_semaphore.cpp b/src/video_core/renderer_vulkan/vk_master_semaphore.cpp
index 6af474304..0445ba28f 100644
--- a/src/video_core/renderer_vulkan/vk_master_semaphore.cpp
+++ b/src/video_core/renderer_vulkan/vk_master_semaphore.cpp
@@ -21,4 +21,21 @@ MasterSemaphore::~MasterSemaphore() {
     device.destroySemaphore(semaphore);
 }
 
+MasterSemaphoreFence::MasterSemaphoreFence(const Instance& instance) : device{instance.GetDevice()} {
+    fence_reserve.resize(FENCE_RESERVE_COUNT);
+    for (vk::Fence& fence : fence_reserve) {
+        fence = device.createFence({});
+    }
+}
+
+MasterSemaphoreFence::~MasterSemaphoreFence() {
+    device.waitIdle();
+    for (const vk::Fence fence : fence_reserve) {
+        device.destroyFence(fence);
+    }
+    for (const Fence& fence : fences) {
+        device.destroyFence(fence.fence);
+    }
+}
+
 } // namespace Vulkan
diff --git a/src/video_core/renderer_vulkan/vk_master_semaphore.h b/src/video_core/renderer_vulkan/vk_master_semaphore.h
index 0f2f352a8..f6ac46ce4 100644
--- a/src/video_core/renderer_vulkan/vk_master_semaphore.h
+++ b/src/video_core/renderer_vulkan/vk_master_semaphore.h
@@ -92,4 +92,129 @@ private:
     std::atomic<u64> current_tick{1}; ///< Current logical tick.
 };
 
+class MasterSemaphoreFence {
+    static constexpr std::size_t FENCE_RESERVE_COUNT = 8;
+public:
+    explicit MasterSemaphoreFence(const Instance& instance);
+    ~MasterSemaphoreFence();
+
+    /// Returns the current logical tick.
+    [[nodiscard]] u64 CurrentTick() const noexcept {
+        return current_tick.load(std::memory_order_acquire);
+    }
+
+    /// Returns the last known GPU tick.
+    [[nodiscard]] u64 KnownGpuTick() const noexcept {
+        return gpu_tick.load(std::memory_order_acquire);
+    }
+
+    /// Attempts to retrieve a reserved fence
+    [[nodiscard]] vk::Fence TryGetReservedFence() {
+        if (fence_reserve.empty()) {
+            return VK_NULL_HANDLE;
+        }
+
+        vk::Fence fence = fence_reserve.back();
+        fence_reserve.pop_back();
+        return fence;
+    }
+
+    /// Returns an available fence for queue submission.
+    [[nodiscard]] vk::Fence Handle() noexcept {
+        vk::Fence fence{};
+        if (fence = TryGetReservedFence(); !fence) {
+            fence = device.createFence({});
+        }
+
+        const u64 tick{CurrentTick()};
+        fences.push_front(Fence{
+            .fence = fence,
+            .gpu_tick = tick
+        });
+        return fence;
+    }
+
+    /// Returns true when a tick has been hit by the GPU.
+    [[nodiscard]] bool IsFree(u64 tick) const noexcept {
+        return KnownGpuTick() >= tick;
+    }
+
+    /// Advance to the logical tick and return the old one
+    [[nodiscard]] u64 NextTick() noexcept {
+        return current_tick.fetch_add(1, std::memory_order_release);
+    }
+
+    /// Returns the tick of the most recent signaled fence
+    [[nodiscard]] u64 FenceCounterValue() {
+        if (fences.empty()) [[unlikely]] {
+            return CurrentTick();
+        }
+
+        u64 tick{KnownGpuTick()};
+        do {
+            Fence fence = fences.back();
+            if (device.getFenceStatus(fence.fence) != vk::Result::eSuccess) {
+                return tick;
+            }
+            tick = fence.gpu_tick;
+            device.resetFences(fence.fence);
+            fence_reserve.push_back(fence.fence);
+            fences.pop_back();
+        } while (!fences.empty());
+
+        return tick;
+    }
+
+    /// Refresh the known GPU tick
+    void Refresh() {
+        u64 this_tick{};
+        u64 counter{};
+        do {
+            this_tick = gpu_tick.load(std::memory_order_acquire);
+            counter = FenceCounterValue();
+            if (counter < this_tick) {
+                return;
+            }
+        } while (!gpu_tick.compare_exchange_weak(this_tick, counter, std::memory_order_release,
+                                                 std::memory_order_relaxed));
+    }
+
+    /// Waits for a tick to be hit on the GPU
+    void Wait(u64 tick) {
+        // No need to wait if the GPU is ahead of the tick
+        if (IsFree(tick)) {
+            return;
+        }
+        // Update the GPU tick and try again
+        Refresh();
+        if (IsFree(tick)) {
+            return;
+        }
+
+        // If none of the above is hit, search for the fence
+        // with the requested tick and wait for it
+        for (const Fence& fence : fences) {
+            if (fence.gpu_tick == tick) {
+                void(device.waitForFences(fence.fence, true, WAIT_TIMEOUT));
+                Refresh();
+                return;
+            }
+        }
+
+        UNREACHABLE_MSG("Attempting to wait for tick {} that has not been submitted", tick);
+    }
+
+private:
+    vk::Device device;
+    std::atomic<u64> gpu_tick{0};     ///< Current known GPU tick.
+    std::atomic<u64> current_tick{1}; ///< Current logical tick.
+
+    struct Fence {
+        vk::Fence fence;
+        u64 gpu_tick;
+    };
+    std::deque<Fence> fences; ///< List of pending fences
+    std::vector<vk::Fence> fence_reserve; ///< Reserve of unsignaled fences
+};
+
 } // namespace Vulkan