From f2e026a1d8fb2384c1ece24e6dd32062b4f390a2 Mon Sep 17 00:00:00 2001
From: Fernando Sahmkow <fsahmkow27@gmail.com>
Date: Mon, 10 Jun 2019 08:36:22 -0400
Subject: [PATCH] gpu_asynch: Simplify synchronization to a simpler
 consumer->producer scheme.

---
 src/video_core/gpu_thread.cpp | 18 +++---------------
 src/video_core/gpu_thread.h   | 32 --------------------------------
 2 files changed, 3 insertions(+), 47 deletions(-)

diff --git a/src/video_core/gpu_thread.cpp b/src/video_core/gpu_thread.cpp
index 6926553957..b87938fdd5 100644
--- a/src/video_core/gpu_thread.cpp
+++ b/src/video_core/gpu_thread.cpp
@@ -21,7 +21,7 @@ static void RunThread(VideoCore::RendererBase& renderer, Tegra::DmaPusher& dma_p
     MicroProfileOnThreadCreate("GpuThread");
 
     // Wait for first GPU command before acquiring the window context
-    state.WaitForCommands();
+    while (state.queue.Empty());
 
     // If emulation was stopped during disk shader loading, abort before trying to acquire context
     if (!state.is_running) {
@@ -32,7 +32,6 @@ static void RunThread(VideoCore::RendererBase& renderer, Tegra::DmaPusher& dma_p
 
     CommandDataContainer next;
     while (state.is_running) {
-        state.WaitForCommands();
         while (!state.queue.Empty()) {
             state.queue.Pop(next);
             if (const auto submit_list = std::get_if<SubmitListCommand>(&next.data)) {
@@ -49,8 +48,7 @@ static void RunThread(VideoCore::RendererBase& renderer, Tegra::DmaPusher& dma_p
             } else {
                 UNREACHABLE();
             }
-            state.signaled_fence = next.fence;
-            state.TrySynchronize();
+            state.signaled_fence.store(next.fence);
         }
     }
 }
@@ -100,22 +98,12 @@ void ThreadManager::FlushAndInvalidateRegion(CacheAddr addr, u64 size) {
 u64 ThreadManager::PushCommand(CommandData&& command_data) {
     const u64 fence{++state.last_fence};
     state.queue.Push(CommandDataContainer(std::move(command_data), fence));
-    state.SignalCommands();
     return fence;
 }
 
 MICROPROFILE_DEFINE(GPU_wait, "GPU", "Wait for the GPU", MP_RGB(128, 128, 192));
 void SynchState::WaitForSynchronization(u64 fence) {
-    if (signaled_fence >= fence) {
-        return;
-    }
-
-    // Wait for the GPU to be idle (all commands to be executed)
-    {
-        MICROPROFILE_SCOPE(GPU_wait);
-        std::unique_lock lock{synchronization_mutex};
-        synchronization_condition.wait(lock, [this, fence] { return signaled_fence >= fence; });
-    }
+    while (signaled_fence.load() < fence);
 }
 
 } // namespace VideoCommon::GPUThread
diff --git a/src/video_core/gpu_thread.h b/src/video_core/gpu_thread.h
index 05a168a726..1d9d0c39e3 100644
--- a/src/video_core/gpu_thread.h
+++ b/src/video_core/gpu_thread.h
@@ -88,41 +88,9 @@ struct CommandDataContainer {
 /// Struct used to synchronize the GPU thread
 struct SynchState final {
     std::atomic_bool is_running{true};
-    std::atomic_int queued_frame_count{};
-    std::mutex synchronization_mutex;
-    std::mutex commands_mutex;
-    std::condition_variable commands_condition;
-    std::condition_variable synchronization_condition;
-
-    /// Returns true if the gap in GPU commands is small enough that we can consider the CPU and GPU
-    /// synchronized. This is entirely empirical.
-    bool IsSynchronized() const {
-        constexpr std::size_t max_queue_gap{5};
-        return queue.Size() <= max_queue_gap;
-    }
-
-    void TrySynchronize() {
-        if (IsSynchronized()) {
-            std::lock_guard lock{synchronization_mutex};
-            synchronization_condition.notify_one();
-        }
-    }
 
     void WaitForSynchronization(u64 fence);
 
-    void SignalCommands() {
-        if (queue.Empty()) {
-            return;
-        }
-
-        commands_condition.notify_one();
-    }
-
-    void WaitForCommands() {
-        std::unique_lock lock{commands_mutex};
-        commands_condition.wait(lock, [this] { return !queue.Empty(); });
-    }
-
     using CommandQueue = Common::SPSCQueue<CommandDataContainer>;
     CommandQueue queue;
     u64 last_fence{};