[Impeller] Adjustments to SubmitKHR and queries.

impeller/renderer/backend/vulkan/context_vk.cc

@@ -4,6 +4,8 @@
 
 #include "impeller/renderer/backend/vulkan/context_vk.h"
 
+#include "fml/concurrent_message_loop.h"
+
 #ifdef FML_OS_ANDROID
 #include <pthread.h>
 #include <sys/resource.h>
@@ -128,6 +130,12 @@ void ContextVK::Setup(Settings settings) {
     return;
   }
 
+  queue_submit_thread_ = std::make_unique<fml::Thread>("QueueSubmitThread");
+  queue_submit_thread_->GetTaskRunner()->PostTask([]() {
+    // submitKHR is extremely cheap and mostly blocks on an internal fence.
+    fml::RequestAffinity(fml::CpuAffinity::kEfficiency);
+  });
+
   raster_message_loop_ = fml::ConcurrentMessageLoop::Create(
       std::min(4u, std::thread::hardware_concurrency()));
   raster_message_loop_->PostTaskToAllWorkers([]() {
@@ -486,6 +494,10 @@ const vk::Device& ContextVK::GetDevice() const {
   return device_holder_->device.get();
 }
 
+const fml::RefPtr<fml::TaskRunner> ContextVK::GetQueueSubmitRunner() const {
+  return queue_submit_thread_->GetTaskRunner();
+}
+
 const std::shared_ptr<fml::ConcurrentTaskRunner>
 ContextVK::GetConcurrentWorkerTaskRunner() const {
   return raster_message_loop_->GetTaskRunner();
@@ -500,6 +512,7 @@ void ContextVK::Shutdown() {
   fence_waiter_.reset();
   resource_manager_.reset();
 
+  queue_submit_thread_->Join();
   raster_message_loop_->Terminate();
 }
 

impeller/renderer/backend/vulkan/context_vk.h

@@ -10,6 +10,7 @@
 #include "flutter/fml/macros.h"
 #include "flutter/fml/mapping.h"
 #include "flutter/fml/unique_fd.h"
+#include "fml/thread.h"
 #include "impeller/base/backend_cast.h"
 #include "impeller/core/formats.h"
 #include "impeller/renderer/backend/vulkan/command_pool_vk.h"
@@ -133,6 +134,18 @@ class ContextVK final : public Context,
   const std::shared_ptr<fml::ConcurrentTaskRunner>
   GetConcurrentWorkerTaskRunner() const;
 
+  /// @brief A single-threaded task runner that should only be used for
+  ///        submitKHR.
+  ///
+  /// SubmitKHR will block until all previously submitted command buffers have
+  /// been scheduled. If there are no platform views in the scene (excluding
+  /// texture backed platform views). Then it is safe for SwapchainImpl::Present
+  /// to return before submit has completed. To do so, we offload the submit
+  /// command to a specialized single threaded task runner. The single thread
+  /// ensures that we do not queue up too much work and that the submissions
+  /// proceed in order.
+  const fml::RefPtr<fml::TaskRunner> GetQueueSubmitRunner() const;
+
   std::shared_ptr<SurfaceContextVK> CreateSurfaceContext();
 
   const std::shared_ptr<QueueVK>& GetGraphicsQueue() const;
@@ -176,6 +189,7 @@ class ContextVK final : public Context,
   std::shared_ptr<CommandPoolRecyclerVK> command_pool_recycler_;
   std::string device_name_;
   std::shared_ptr<fml::ConcurrentMessageLoop> raster_message_loop_;
+  std::unique_ptr<fml::Thread> queue_submit_thread_;
   std::shared_ptr<GPUTracerVK> gpu_tracer_;
 
   bool sync_presentation_ = false;

impeller/renderer/backend/vulkan/gpu_tracer_vk.cc

@@ -16,7 +16,7 @@
 
 namespace impeller {
 
-static constexpr uint32_t kPoolSize = 64u;
+static constexpr uint32_t kPoolSize = 1024u;
 
 GPUTracerVK::GPUTracerVK(const std::shared_ptr<DeviceHolder>& device_holder)
     : device_holder_(device_holder) {

impeller/renderer/backend/vulkan/swapchain_impl_vk.cc

@@ -522,7 +522,7 @@ bool SwapchainImplVK::Present(const std::shared_ptr<SwapchainImageVK>& image,
   if (context.GetSyncPresentation()) {
     task();
   } else {
-    context.GetConcurrentWorkerTaskRunner()->PostTask(task);
+    context.GetQueueSubmitRunner()->PostTask(task);
   }
   return true;
 }

impeller/renderer/context.h

@@ -175,7 +175,9 @@ class Context {
   ///
   ///             This is required for correct rendering on Android when using
   ///             the hybrid composition mode. This has no effect on other
-  ///             backends.
+  ///             backends. This is analogous to the check for isMainThread in
+  ///             surface_mtl.mm to block presentation on scheduling of all
+  ///             pending work.
   virtual void SetSyncPresentation(bool value) {}
 
   //----------------------------------------------------------------------------