How to schedule copies on transfer queue with a semaphore? - c++

Question

I am aiming to use vkCmdCopyBuffer with a transfer queue that is signaled via semaphore from a compute shader queue. The compute shader is running on a graphics queue and is intended to signal the transfer queue to copy to host and also to signal the render. My goal is to have the copy to host done on a different queue to the graphics queue.
I am currently getting the error message:
VULKAN> ERROR(violation): Validation Error: [ UNASSIGNED-CoreValidation-DrawState-QueueForwardProgress ] Object 0: handle = 0x301e6c0000000022, type = VK_OBJECT_TYPE_SEMAPHORE; Object 1: handle = 0x21d51d0ac80, type = VK_OBJECT_TYPE_QUEUE; Object 2: handle = 0x21d51d0ac80, type = VK_OBJECT_TYPE_QUEUE; | MessageID = 0xe825f293 | vkQueueSubmit(): pSubmits[0].pSignalSemaphores[1] is signaling VkQueue 0x21d51d0ac80[] (VkSemaphore 0x301e6c0000000022[]) that was previously signaled by VkQueue 0x21d51d0ac80[] but has not since been waited on by any queue.
The compute shader is submit with:
void Renderer::runCompute()
{
VkSemaphore waitSemaphores[] = { mComputeReadySemaphore };
VkSemaphore signalSemaphores[] = { mComputeFinishedSemaphoreGraphics, mComputeFinishedSemaphoreTransfer };
VkPipelineStageFlags waitStages[] = { VK_PIPELINE_STAGE_COMPUTE_SHADER_BIT };
VkSubmitInfo submitInfo{};
submitInfo.sType = VK_STRUCTURE_TYPE_SUBMIT_INFO;
if (mHasDispatchedCompute) [[likely]]
{
submitInfo.waitSemaphoreCount = ARR_LEN(waitSemaphores);
submitInfo.pWaitSemaphores = waitSemaphores;
submitInfo.pWaitDstStageMask = waitStages;
}
else
{
mHasDispatchedCompute = true;
}
submitInfo.signalSemaphoreCount = ARR_LEN(signalSemaphores);
submitInfo.pSignalSemaphores = signalSemaphores;
submitInfo.commandBufferCount = 1;
submitInfo.pCommandBuffers = &mComputeCommandBuffer;
if (vkQueueSubmit(mpGraphicsQueue, 1, &submitInfo, VK_NULL_HANDLE) != VK_SUCCESS)
throw std::runtime_error("Failed to submit command buffer!");
}
And the transfer queue is submit with:
void Renderer::runTransfer()
{
VkSemaphore waitSemaphores[] = { mComputeFinishedSemaphoreTransfer };
VkPipelineStageFlags waitStages[] = { VK_PIPELINE_STAGE_ALL_COMMANDS_BIT };
VkSubmitInfo submitInfo{};
submitInfo.sType = VK_STRUCTURE_TYPE_SUBMIT_INFO;
if (mHasDispatchedTransfer) [[likely]]
{
submitInfo.waitSemaphoreCount = ARR_LEN(waitSemaphores);
submitInfo.pWaitSemaphores = waitSemaphores;
submitInfo.pWaitDstStageMask = waitStages;
}
else
{
mHasDispatchedTransfer = true;
}
submitInfo.commandBufferCount = 1;
submitInfo.pCommandBuffers = &mTransferCommandBuffer;
if (vkQueueSubmit(mpTransferQueue, 1, &submitInfo, mTransferReadFence) != VK_SUCCESS)
throw std::runtime_error("Failed to submit command buffer!");
}
And called here:
constexpr uint32_t SINGLE_FRAME_RENDERING = 0;
vkWaitForFences(mpLogicDevice, 1, &mTransferReadFence, VK_TRUE, UINT64_MAX);
updateFrame(SINGLE_FRAME_RENDERING);
vkResetFences(mpLogicDevice, 1, &mTransferReadFence);
runCompute();
runTransfer();
auto imageIndex = prepareFrame();
// Submit the command buffer
VkSubmitInfo submitInfo{};
submitInfo.sType = VK_STRUCTURE_TYPE_SUBMIT_INFO;
VkSemaphore waitSemaphores[] = { mImageAvailableSemaphores[SINGLE_FRAME_RENDERING], mComputeFinishedSemaphoreGraphics };
VkPipelineStageFlags waitStages[] = { VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT, VK_PIPELINE_STAGE_FRAGMENT_SHADER_BIT };
submitInfo.waitSemaphoreCount = ARR_LEN(waitSemaphores);
submitInfo.pWaitSemaphores = waitSemaphores;
submitInfo.pWaitDstStageMask = waitStages;
submitInfo.commandBufferCount = 1;
submitInfo.pCommandBuffers = &mGraphicsCommandBuffers[createCommandBuffersOnce() ? imageIndex : SINGLE_FRAME_RENDERING];
VkSemaphore signalSemaphores[] = { mRenderFinishedSemaphores[SINGLE_FRAME_RENDERING], mComputeReadySemaphore };
submitInfo.signalSemaphoreCount = ARR_LEN(signalSemaphores);
submitInfo.pSignalSemaphores = signalSemaphores;
if (vkQueueSubmit(mpGraphicsQueue, 1, &submitInfo, mInFlightFences[SINGLE_FRAME_RENDERING]) != VK_SUCCESS)
throw std::runtime_error("Failed to submit draw command buffer!");
submitFrame(signalSemaphores, imageIndex);
Where updateFrame() is a host manipulation of the buffer, prepareFrame() is swap chain image acquisition and submitFrame() calls vkQueuePresentKHR().

Answer 1

if(mHasDispatchedTransfer) may remove the wait on the semaphore mComputeFinishedSemaphoreTransfer, but the semaphore is unconditionally signaled in runCompute(). That will lead to the semaphore being signaled repeatedly without no wait inbetween if mHasDispatchedTransfer is false.