Entries for tag "vulkan", ordered from most recent. Entry count: 22.
# Human-friendly classification of Vulkan resources
In graphics programming we deal with different kinds of resources. Their specific types and names depend on graphics API. For example, in Direct3D 9 we have vertex buffers, index buffers, constant buffers, textures etc. OpenGL equivalent of constant buffer is uniform buffer object (UBO).
Vulkan has only two types of resources: buffers and images. This may be the only thing that is simpler in Vulkan than in other APIs :) When creating such resource, we specify usage flags that define how do we intend to use it. For example,
VK_BUFFER_USAGE_VERTEX_BUFFER_BIT means that a buffer may be used as vertex buffer.
VK_IMAGE_USAGE_COLOR_ATTACHMENT_BIT means that an image may be used as color attachment (which is Vulkan name for “render target”).
Such flags may be combined together, so a single buffer can contain data to be used as vertex buffer, index buffer, and uniform buffer. I’m not 100% sure if this is guaranteed by the specification (theoretically some drivers could return disjoint sets of
VkMemoryRequirements::memoryTypeBits for different usage flags), but I think that every real implementation allows that. It means we cannot clearly classify buffers and images into categories. Despite that, I decided to develop a human-friendly classification of Vulkan resources into several categories, starting from most “special”, and ending with most “common/generic” ones. I propose following algorithm:
For buffers: // Buffer is used as source of data for fixed-function stage of graphics pipeline. // It’s indirect, vertex, or index buffer. if ((usage & (VK_BUFFER_USAGE_INDIRECT_BUFFER_BIT | VK_BUFFER_USAGE_VERTEX_BUFFER_BIT | VK_BUFFER_USAGE_INDEX_BUFFER_BIT)) != 0) return class0; // Buffer is accessed by shaders for load/store/atomic. // Aka “UAV” else if ((usage & (VK_BUFFER_USAGE_STORAGE_BUFFER_BIT | VK_BUFFER_USAGE_STORAGE_TEXEL_BUFFER_BIT)) != 0) return class1; // Buffer is accessed by shaders for reading uniform data. // Aka “constant buffer” else if ((usage & (VK_BUFFER_USAGE_UNIFORM_BUFFER_BIT | VK_BUFFER_USAGE_UNIFORM_TEXEL_BUFFER_BIT)) != 0) return class2; // Any other type of buffer. // Notice that VK_BUFFER_USAGE_TRANSFER_SRC_BIT and VK_BUFFER_USAGE_TRANSFER_DST_BIT // flags are intentionally ignored. else return class3; For images: // Image is used as depth/stencil “texture/surface”. if ((usage & VK_IMAGE_USAGE_DEPTH_STENCIL_ATTACHMENT_BIT) != 0) return class0; // Image is used as other type of attachment. // Aka “render target” else if ((usage & (VK_IMAGE_USAGE_INPUT_ATTACHMENT_BIT | VK_IMAGE_USAGE_TRANSIENT_ATTACHMENT_BIT | VK_IMAGE_USAGE_COLOR_ATTACHMENT_BIT)) != 0) return class1; // Image is accessed by shaders for sampling. // Aka “texture” else if ((usage & VK_IMAGE_USAGE_SAMPLED_BIT) != 0) return class2; // Any other type of image. // Notice that VK_IMAGE_USAGE_TRANSFER_SRC_BIT and VK_IMAGE_USAGE_TRANSFER_DST_BIT // flags are intentionally ignored. else return class3;
I needed this because I wanted to introduce better coloring to VMA Dump Vis. Vulkan Memory Allocator (VMA) is a C++ library that simplifies GPU memory management in Vulkan applications. VMA Dump Vis is a Python script that can visualize JSON dump from this library on a picture. As I updated the library to remember usage flags of created resources, I wanted to use them to show more information on the picture. To do this, I defined following color scheme:
Example visualization of Vulkan memory in some game:
This color scheme is carefully designed. I based it on following principles:
VK_IMAGE_TILING_OPTIMALshould be used wherever possible, so those with
VK_IMAGE_TILING_LINEARare just marked with green. Images of unknown tiling have color between cyan and green.
You can already visualize your Vulkan memory with all these colors if you grab Vulkan Memory Allocator from development branch. I think that this classification of GPU resources and accompanying color scheme could also be useful for other graphics APIs.
# Vulkan API - my talk at Warsaw University of Technology
On Wednesday 16 April, around 8 PM, at Warsaw University of Technology, during weekly meeting of KNTG Polygon, I will give a talk about "Vulkan API" (in Polish). Come if you want to hear about new generation of graphics APIs, see how Vulkan API looks like, what tools are there to support it, what are advantages and disadvantages of using such API and finally decide whethere learning Vulkan is a good idea for you.
Event on Facebook: https://www.facebook.com/events/185314825611839/
# Memory management in Vulkan and DX12: slides are online
Slides from my talk at Game Developers Conference (GDC) 2018: "Memory management in Vulkan and DX12" are now available online, as part of materials from Advanced Graphics Techniques Tutorial. Access to this PDF is open to anyone, not behind GDC Vault paywall. I've put some additional information in "backup" slides at the end that I didn't show during my presentation. The slides are designed the way that you can learn from them even without seeing the talk.
Update 2018-05-04: Slides from my talk in PPTX format with additional notes are now available (together with many other GDC 2018 presentations) on page: GDC 2018 Presentations - GPUOpen.
# Debugging Vulkan driver crash - equivalent of NVIDIA Aftermath
New generation, explcit graphics APIs (Vulkan and DirectX 12) are more efficient, involve less CPU overhead. Part of it is that they don't check most errors. In old APIs (Direct3D 9, OpenGL) every function call was validated internally, returned success of failure code, while driver crash indicated a bug in driver code. New APIs, on the other hand, rely on developer doing the right thing. Of course some functions still return error code (especially ones that allocate memory or create some resource), but those that record commands into a command buffer just return
void. If you do something illegal, you can expect undefined behavior. You can use Validation Layers / Debug Layer to do some checks, but otherwise everything may work fine on some GPUs, you may get incorrect result, or you may experience driver crash or timeout (called "TDR"). Good thing is that (contrary to old Windows XP), crash inside graphics driver doesn't cause "blue screen of death" or machine restart. System just restarts graphics hardware and driver, while your program receives
VK_ERROR_DEVICE_LOST code from one of functions like
vkQueueSubmit. Unfortunately, you then don't know which specific draw call or other command caused the crash.
NVIDIA proposed solution for that: they created NVIDIA Aftermath library. It lets you (among other things) record commands that write custom "marker" data to a buffer that survives driver crash, so you can later read it and see which command was successfully executed last. Unfortunately, this library works only with NVIDIA graphics cards and only in D3D11 and D3D12.
I was looking for similar solution for Vulkan. When I saw that Vulkan can "import" external memory, I thought that maybe I could use function
vkCmdFillBuffer to write immediate value to such buffer and this way implement the same logic. I then started experimenting with extensions: VK_KHR_get_physical_device_properties_2, VK_KHR_external_memory_capabilities, VK_KHR_external_memory, VK_KHR_external_memory_win32, VK_KHR_dedicated_allocation. I was basically trying to somehow allocate a piece of system memory and import it to Vulkan to write to it as Vulkan buffer. I tried many things:
HeapAlloc and other ways, with various flags, but nothing worked for me. I also couldn't find any description or sample code of how these extensions could be used in Windows to import some system memory as Vulkan buffer.
Everything changed when I learned that creating normal device memory and buffer inside Vulkan is enough! It survives driver crash, so its content can be read later via mapped pointer. No extensions required. I don't think this is guaranteed by specification, but it seems to work on both AMD and NVIDIA cards. So my current solution to write makers that survive driver crash in Vulkan is:
VkDeviceMemoryfrom memory type that has
HOST_VISIBLE + HOST_COHERENTflags. (This is system RAM. Spec guarantees that you can always find such type.)
vkMapMemoryto get raw CPU pointer to its data.
VK_BUFFER_USAGE_TRANSFER_DST_BITand bind it to that memory using
vkCmdFillBufferto write immediate data with your custom "markers" to the buffer.
VK_ERROR_DEVICE_LOST), read data under the pointer to see what marker values were successfully written last and deduce which one of your commands might cause the crash.
There is also a new extension available on latest AMD drivers: VK_AMD_buffer_marker. It adds just one function:
vkCmdWriteBufferMarkerAMD. It works similar to beforementioned
vkCmdFillBuffer, but it adds two good things that let you write your markers with much better granularity:
vkCmdFillBuffermust be called outside render pass.
I created a simple library that implements all this logic under easy interface, which I called "Vulkan AfterCrash". All you need to use it is just this single file: VulkanAfterCrash.h.
Update 4 April 2018: In GDC 2018 talk "Aftermath: Advances in GPU Crash Debugging (Presented by NVIDIA)", Alex Dunn announced that a Vulkan extension from NVIDIA will also be available, called VK_NV_device_diagnostic_checkpoints, but I can see it's not publicly accessible yet.
Update 1 August 2018: Documentation for extension VK_NV_device_diagnostic_checkpoints has been published in Vulkan version 1.1.82.
Update 12 September 2018: I've created similar, portable library for Direct3D 12 - see blog post "Debugging D3D12 driver crash".
# Vulkan Memory Allocator 2.0.0
At Game Developers Conference (GDC) last week I released final version 2.0.0 of Vulkan Memory Allocator library. It is now well documented and thanks to contributions from open source community it compiles and works on Windows, Linux, Android, and MacOS. Together with it I released VMA Dump Vis - a Python script that visualizes Vulkan memory on a picture. From now on I will continue incremental development on "development" branch and occasionally merge to "master". Feel free to contact me if you have any feedback, suggestions or if you find a bug.
# Memory management in Vulkan and DX12 - my talk at GDC 2018
If you happen to come to this year's Game Developers Conference (GDC), I'd like to invite you to my talk: "Memory management in Vulkan and DX12". During this lecture I will not only advertise my Vulkan Memory Allocator library, but I will also show technical details, tips and tricks for GPU memory management that you can use on your own when programming using Vulkan or Direct3D 12.
# VK_KHR_dedicated_allocation unofficial manual
I wrote a short article that explains how to use Vulkan extenion "VK_KHR_dedicated_allocation". It may be interesting to you if you are a programmer and you code graphics using Vulkan.
Go to article: VK_KHR_dedicated_allocation unofficial manual
# Vulkan Memory Allocator 2.0.0-alpha.3
I just published new version of Vulkan Memory Allocator 2.0.0-alpha.3. I'm quite happy with the quality of this code. Documentation is also updated, so if nothing else, please just go see User guide. I still marked it as "alpha" because I would like to ask for feedback and I may still change everything.
I would like to discuss proposed terminology. Naming things in code is a hard problem in general, and especially as English is not my native language, so please fill free to contact me and propose more elegant names to what I called: allocator, allocation, pool, block, stats, free range, used/unused bytes, own memory, persistently mapped memory, pointer to mapped data, lost allocation (becoming lost, making other lost), defragmentation, and used internally: suballocation, block vector.