February 2018

# Switchable graphics versus D3D11 adapters

00:34
Sat
24
Feb 2018

When you have a laptop with so called "switchable graphics" (like I do in my Lenovo IdeaPad G50-80), you effectively have two GPUs. In my case, these are: Intel i7-5500U and AMD Radeon R5 M330. While programming in DirectX 11, you can enumerate these two adapters and choose any of them while creating a ID3D11Device object. For quite some time I was wondering how various settings of this "switchable graphics" affect my app? Today I finally figured it out. Long story short: They just change order of these adapters as visible to my program, so that the appropriate one is visible as adapter 0. Here is the full story:

It looks like the base setting is the one that can be found in Windows Settings > Power options > edit your power plan > Switchable Dynamic Graphics. (Not to confuse with "AMD Graphics Power Settings"!) When you set it to "Optimize power savings" or "Optimize performance", application sees Intel GPU as first adapter:

When you choose "Maximize performance", application sees AMD GPU as first adapter:

I also found that Radeon Settings (the app that comes with AMD graphics driver) overrides this system setting. If you go to System > Switchable Graphics and make configuration for your specific executable, then again: choosing "Power Saving" makes your app see Intel GPU as first adapter, while choosing "High Performance" makes AMD graphics first.

It's as simple as that. Basically if you always use the first adapter you find, then you follow recommended settings of the system. You are still free to use the other adapter while creating your D3D11 device. I checked that - it works and it really uses that one.

It's especially important if you meet a strange bug where your app hangs on one of these GPUs.

Update 2018-05-02: Microsoft plans to add an API for enumerating adapters based on a given GPU preference (minimum power or high performance). See IDXGIFactory6::EnumAdapterByGpuPreference.

Comments | #directx Share

# Memory management in Vulkan and DX12 - my talk at GDC 2018

11:26
Wed
21
Feb 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.

List of presentations made by my colleagues at AMD can be found here: GDC 2018 Presentations - GPUOpen, and list of all GDC talks is available as Session Scheduler on gdconf.com.

Comments | #vulkan #directx #gdc #events #teaching Share

# When integrated graphics works better

10:36
Sat
17
Feb 2018

In RPG games the more powerful your character is, the more tough and scary are the monsters you have to fight. I sometimes get a feeling that the same applies to real life - bugs you meet when you are a programmer. I recently blogged about the issue when QueryPerformanceCounter call takes long time. I've just met another weird problem. Here is my story:

I have Lenovo IdeaPad G50-80 (80E502ENPB) laptop. It has switchable graphics: integrated Intel i7-5500U and dedicated AMD Radeon R5 M330. Of course I used to choose AMD dedicated graphics, because it's more powerful. My application is a music visualization program. It renders graphics using Direct3D 11. It uses one ID3D11Device object and one thread for rendering, but two windows displayed on two outputs: output 1 (laptop screen) contains window with GUI and preview, while output 2 (projector connected via VGA or HDMI) shows main view using borderless, topmost window covering whole screen (but not real fullscreen as in IDXGISwapChain::​SetFullscreenState). I tend to enable V-sync on output 1 (IDXGISwapChain::​Present SyncInterval = 1) and disable it on output 0 (SyncInterval = 0). My rendering algorithm looks like this:

Loop over frames:
    Render scene to MainRenderTarget
    Render MainRenderTarget to OutputBackBuffer, covering whole screen
    Render MainRenderTarget to PreviewBackBuffer, on a quad
    Render ImGui to PreviewBackBuffer
    OutputSwapChain->Present()
    PreviewSwapChain->Present()

So far I had just one problem with it: my framerate decreased over time. It used to drop very quickly after launching the app from 60 to 30 FPS and stabilize there, but after few hours it was steadily decreasing to 20 FPS or even less. I couldn't identify the reason for it in my code, like a memory leak. It seemed to be related to rendering. I could somehow live with this issue - low framerate was not that noticable.

Suddenly this Thursday, when I wanted to test new version of the program, I realized it hangs after around a minute from launching. It was a strange situation in which the app seemed to be running normally, but it was just not rendering any new frames. I could see it still works by inspecting CPU usage and thread list with Process Hacker. I could minimize its windows or cover them by other windows and they preserved their content after restoring. I even captured trace in GPUView, only to notice that the app is filling DirectX command queue and AMD GPU is working. Still, nothing was rendered.

That was a frightening situation for me, because I need to have it working for this weekend. After I checked that restarting app or the whole system doesn't help, I tried to identify the cause and fix it in various ways:

1. I thought that maybe there is just some bug in the new version of my program, so I launched the previous version - one that successfully worked before, reaching more than 10 hours of uptime. Unfortunately, the problem still occured.

2. I thought that maybe it's a bug in the new AMD graphics driver, so I downloaded and installed previous version, performing "Clean install". It didn't help either.

3. In desperation, I formatted whole hard drive and reinstalled operating system. I planned to to it anyway, because it was a 3-year-old system, upgraded from Windows 8 and I had some other problems with it (that I don't describe here because they were unrelated to graphics). I installed the latest, clean Windows 10 with latest updates and all the drivers. Even that didn't solve my problem. The program still hung soon after every launch.

I finally came up with an idea to switch my app to using Intel integrated graphics. It can be done in Radeon Settings > "Switchable Graphics" tab. In a popup menu for a specific executable, "High Performance" means choosing dedicated AMD GPU and "Power Saving" means choosing integrated Intel GPU. See article Configuring Laptop Switchable Graphics... for details.

It solved my problem! The program not only doesn't hang any longer, but it also maintains stable 60 FPS now (at least it did during my 2h test). Framerate drops only when there is a scene that blends many layers together on a FullHD output - apparently this GPU cannot keep up with drawing so many pixels per second. Anyway, this is the situation where using integrated Intel graphics turns out work better than a faster, dedicated GPU.

I still don't know what is the cause of this strange bug. Is it something in the way my app uses D3D11? Or is it a bug in graphics driver (one of the two I need to have installed)? I'd like to investigate it further when I find some time. For now, I tend to believe that:

- The only thing that might have changed recently and break my app was some Windows updated pushed by Microsoft.

- The two issues: the one that I had before with framerate decreasing over time and the new one with total image freeze are related. They may have something to do with switchable graphics - having two different GPUs in the system, both enabled at the same time. I suspect that maybe when I want to use Radeon, the outputs (or one of them) are connected to Intel anyway, so the image needs to be copied and synchronized with Intel driver.

Update 2018-02-21: Later after I published this post, I tried few other things to fix the problem. For example, I updated AMD graphics driver to latest version 18.2.2. It didn't help. Suddently, the problem disappeared as mysteriously as it appeared. It happened during a single system launch, without a restart. My application was hunging, and later it started working properly. The only thing that I can remember doing in between was downloading and launching UIforETW - a GUI tool for capturing Event Tracing for Windows (ETW) traces, like the ones for GPUView. I know that it automatically installs GPUView and other necessary tools on first launch, so that may have changed something in my system. Either way, now my program works on AMD graphics without a hang, reaching few hours of uptime and maintaining 60 FPS, which only sometimes drops to 30 FPS, but it also go back up.

Comments | #directx #gpu #windows Share

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