I have 2 graphics applications for OpenGL and Vulkan.
OpenGL loop looks something like this:
glClear(GL_DEPTH_BUFFER_BIT | GL_COLOR_BUFFER_BIT);
static int test = 0;
// "if" statement here is to ensure that there is no any caching or optimizations
// made by OpenGL driver (if such things exist),
// and commands are re-recorded to the buffer every frame
if ((test = 1 - test) == 0) {
glBindBuffer(GL_ARRAY_BUFFER, vertex_buffer1);
glUseProgram(program1);
glDrawArrays(GL_TRIANGLES, 0, vertices_size);
glUseProgram(0);
}
else {
glBindBuffer(GL_ARRAY_BUFFER, vertex_buffer2);
glUseProgram(program2);
glDrawArrays(GL_LINES, 0, vertices_size);
glUseProgram(0);
}
glfwSwapBuffers(window);
And Vulkan:
static uint32_t image_index = 0;
vkAcquireNextImageKHR(device, swapchain, 0xFFFFFFFF, image_available_semaphores[image_index], VK_NULL_HANDLE, &image_indices[image_index]);
vkWaitForFences(device, 1, &submission_completed_fences[image_index], VK_TRUE, 0xFFFFFFFF);
// VK_COMMAND_BUFFER_USAGE_ONE_TIME_SUBMIT_BIT
vkBeginCommandBuffer(cmd_buffers[image_index], &command_buffer_bi);
vkCmdBeginRenderPass(cmd_buffers[image_index], &render_pass_bi[image_index], VK_SUBPASS_CONTENTS_INLINE);
vkCmdEndRenderPass(cmd_buffers[image_index]);
vkEndCommandBuffer(cmd_buffers[image_index]);
vkResetFences(device, 1, &submission_completed_fences[image_index]);
vkQueueSubmit(graphics_queue, 1, &submit_info[image_index], submission_completed_fences[image_index]);
present_info[image_index].pImageIndices = &image_indices[image_index];
vkQueuePresentKHR(present_queue, &present_info[image_index]);
const static int max_swapchain_image_index = swapchain_image_count - 1;
if (++image_index > max_swapchain_image_index) {
image_index = 0;
}
In the Vulkan loop there are no even rendering commands, just empty render pass. Validation layers are disabled.
OpenGL FPS is about 10500, and Vulkan FPS is about 7500 (with 8 swapchain images in use with VK_PRESENT_MODE_IMMEDIATE_KHR, less images make FPS lower).
Code is running on laptop with Ubuntu 18.04, discrete GPU Nvidia RTX 2060, Nvidia driver 450.66, Vulkan API version 1.2.133.
I know that OpenGL driver is highly optimized, but i can't imagine what else is to be optimized in Vulkan loop to make it faster than it is.
Are there some low-level linux driver issues? Or maybe Vulkan performance increase is accomplished only in much more complex applications (using multithreading e.g.)?
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