Vulkan: Add feature flag to flush at framebuffer boundary

include/platform/FeaturesVk.h

@@ -515,6 +515,12 @@ struct FeaturesVk : FeatureSetBase
         "forceFragmentShaderPrecisionHighpToMediump", FeatureCategory::VulkanWorkarounds,
         "Forces highp precision in fragment shader to mediump.", &members,
         "https://issuetracker.google.com/184850002"};
+
+    // Whether we should submit at each FBO boundary.
+    Feature preferSubmitAtFBOBoundary = {
+        "preferSubmitAtFBOBoundary", FeatureCategory::VulkanWorkarounds,
+        "Submit commands to driver at each FBO boundary for performance improvements.", &members,
+        "https://issuetracker.google.com/187425444"};
 };
 
 inline FeaturesVk::FeaturesVk()  = default;

src/libANGLE/renderer/vulkan/ContextVk.cpp

@@ -3477,7 +3477,12 @@ angle::Result ContextVk::syncState(const gl::Context *context,
                 // open, such as invalidate or blit. Note that we always start a new command buffer
                 // because we currently can only support one open RenderPass at a time.
                 onRenderPassFinished();
-
+                if (mRenderer->getFeatures().preferSubmitAtFBOBoundary.enabled)
+                {
+                    // This will behave as if user called glFlush, but the actual flush will be
+                    // triggered at endRenderPass time.
+                    mHasDeferredFlush = true;
+                }
                 gl::Framebuffer *drawFramebuffer = glState.getDrawFramebuffer();
                 mDrawFramebuffer                 = vk::GetImpl(drawFramebuffer);
                 mDrawFramebuffer->setReadOnlyDepthFeedbackLoopMode(false);

src/libANGLE/renderer/vulkan/RendererVk.cpp

@@ -2438,6 +2438,11 @@ void RendererVk::initFeatures(DisplayVk *displayVk,
     // tests to fail.
     ANGLE_FEATURE_CONDITION(&mFeatures, forceFragmentShaderPrecisionHighpToMediump, false);
 
+    // Testing shows that on ARM GPU, doing implicit flush at framebuffer boundary improves
+    // performance. Most app traces shows frame time reduced and manhattan 3.1 offscreen score
+    // improves 7%.
+    ANGLE_FEATURE_CONDITION(&mFeatures, preferSubmitAtFBOBoundary, isARM);
+
     angle::PlatformMethods *platform = ANGLEPlatformCurrent();
     platform->overrideFeaturesVk(platform, &mFeatures);