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Using the Chrome OS* graphics stack on Intel-based Linux* desktops

BY Joone Hur ON Jun 20, 2018

Overview

Chromebook* graphics performance has improved due to the graphics acceleration features provided by Intel® Atom® and Intel® Celeron® System on a Chip (SoC) processors. These features, which include zero-copy texture upload, hardware overlay/atomic pageflip, and video encoding/decoding, enable Intel Chromebooks to achieve better performance, save system memory, and extend battery life.

The interesting thing is that many embedded devices have built their own complicated user interface using web technology because the computing power is enough to run a web engine. Many new web technologies such as HTML5 and device APIs also allow developers to access hardware components and sensors on devices. However, there are still limitations: web applications are not as responsive as native applications. Using 4K video, WebGL, and CSS animations are limited due to the slow performance.

This article describes the hardware acceleration features that are available on the Intel Chromebooks. It also explains how to use the graphics stack on Intel-based Linux systems to improve the performance of your web applications.

New graphics architecture in Chrome OS (2015)

In 2015, Google* released Freon, a new graphics stack that runs on Intel Chromebooks and eliminates the X-Window* dependency to provide better performance and lower power consumption and memory usage. To achieve this, Google and Intel worked together to use the hardware acceleration features available in Intel-based Chromebooks. 

 

Ozone

Google wanted to enable GPU accelerations and run Chromium on multiple platforms such as Linux, Windows*, MacOS*, and embedded systems. As a result, the Ozone layer was introduced into Chromium, which easily separates event handling and surface acceleration. ozone-gbm is part of an effort that was originally designed for Chrome OS to remove X11. It allows Chromium to run on embedded systems and new X11-alternative Windows systems such as Wayland* or Mir*. Currently, there are three backends of Ozone: X11, Wayland, and DRM, as shown in the following diagram. 

Ozone-gbm

Ozone-gbm is one of the Ozone backends that allows ChromeOS to interact directly with DRM/KMS and evdev to remove the X11 dependency. As shown in the following diagram, mini-gbm is a library of user-level APIs used to allocate a buffer directly to the GPU memory accessible by a rendering process. It is easier to enable Intel graphics features such as texture zero-copy, hardware overlay, and video decoding via ozone-gbm. Chrome OS also uses the mode-setting to change the display mode and align events from evdev and painting with vsync signal generated by GPU.

History

The team that created the ozone-wayland project also worked on ozone-gbm for Linux desktop. A blog article was posted on this site to introduce this work. I took over this work to continue to support ozone-gbm with hardware accelerations for Linux desktop. It was not easy to get ozone-gbm to run on desktop Linux because the Chrome OS architecture was significantly changed when Servicification was introduced. I successfully ran the Chromium browser in M58 using mojo UI service (MUS) with ozone-gbm on Yocto Linux. Refer to the details at ozone-dev mailing list.

Why ozone-gbm for Linux Systems?

Many Linux systems have adopted Web technologies, therefore the Chromium browser has become a de facto standard for Linux based devices. However, because most devices have low graphics performance in hardware, they are limited to rendering CSS transforms/transition/animations, WebGL, and video playback. In addition, single web applications don’t need a windowing system, however, a windowing system (for example, X-Window or Wayland) is required to launch the Chromium browser on Linux systems. 

  

Ozone-gbm was introduced in Chrome OS, which has been highly optimized for Intel-based Chromebooks, but can also be used on Intel-based Linux systems. Therefore, we are able to improve the graphics performance of Web applications by providing a way to run ozone-gbm using hardware acceleration features on Linux systems.

Why ozone-gbm on Intel GPU?

Intel and Google have supported modern graphics systems through ozone-gbm on Chromebooks that provides a hardware compositor, atomic pageflip, hardware overlay, and video encode/decode for Intel GPUs (graphics processing units).

As a result, Chromium has enabled the following features such as zero-copy texture uploads for 2D rendering, video acceleration for HTML5 video/WebRTC, and hardware overlay for video, Android* apps, and WebGL. Let’s take a look at each feature in more detail.

Intel graphics features: zero-copy texture upload

Typically, we must perform one copy to upload a bitmap to GPU memory because the GPU memory is separate from the main memory, which can hurt overall performance and use more memory. However, in Intel architecture containing integrated Processor Graphics, we can share the same physical memory between CPU and GPU, allowing a renderer process to paint content on an imported GPU buffer via VGEM that allows a non-privileged user process to map a previously allocated graphics buffer. This feature is called zero-copy texture upload and it provides significant performance benefits and reduces memory footprint. It is only supported on Intel-based Chromebooks.

 

Estimated performance results

Our team estimated performance test results for zero-copy texture upload, as shown below:

Test page Software fallback Zero-copy texture upload Results
http://browsertests.herokuapp.com/perf/background_color_animation.html 5.3 fps 22.3 fps 4.2X faster
https://codepen.io/cubix4u/pen/KXpKRe 12.2 fps 48.2 fps 3.95X faster

* Disclaimer: These values are estimates and are not official benchmark results.

In some cases, zero-copy texture upload is almost 4 times faster than the software fallback. Generally, it is 30~40% faster.

Estimated memory consumption

Our team estimated memory consumption for zero-copy texture upload, as shown below:

Test page Software fallback Zero-copy texture upload Results
http://browsertests.herokuapp.com/perf/background_color_animation.html 80 MB 48 MB 40% lower

* Disclaimer: These values are estimates and are not official benchmark results.

Zero-copy texture uploads are more effective in terms of memory consumption and power savings. For Chrome OS, the memory usage of the GPU process is about 65% lower than the software fallback in native zero-copy. The memory consumed by the renderer process is about 20% lower in native zero-copy.

Intel graphics features: video/image accelerations

The following table shows all the codecs supported by Intel SoCs for each generation. As you can see, the latest Intel® Atom® and Intel® Core® processors, listed below by their codenames, support all hardware codecs that are enabled for Intel-based Chromebooks.

Codec

Braswell / Cherry Trail (Gen8)

Skylake (6th, Gen9)

Apollo Lake

Kaby Lake (7th) / Gemini Lake Coffee Lake (8th)  (Gen9.5)

H.264

Yes

Yes

Yes

Yes

VC-1

Decode only

Decode only

Decode only

Decode only

JPEG

Yes

Yes

Yes

Yes

VP8

Yes

Yes

Yes

Yes

HEVC

Decode only

Yes

Yes

Yes

HEVC 10-bit

No

No

Decode only (8K)

Yes

VP9

No

No

Decode only (4K)

Yes

Estimated performance test: video decoding, Intel Compute stick (Atom)

The Intel® Atom® processor is not as powerful as the Intel® Core® series, so it is important to use the hardware codecs. As you can see in the following table, FPS of hardware accelerated video is estimated at 1.7~3.6 times higher, so you can play larger videos (2K, 4K).

Note: Results were estimated using an Intel Compute stick X5-Z8300 (codenamed Cherry Trail, Gen8 graphics, GPU RAM 512MB). 

Test page Software fallback Hardware accelerated
(video decoding, zero-copy texture upload)
Results
H.264 video 2K (vimeo video) 13.6 fps 24 fps 1.7X higher
H.264 video 4K (vimeo video) 5.7 fps 20.7 fps 3.95X higher
VP9 1K (Youtube)
Uses software decoding
30 fps 30 fps  
VP9 2K (Youtube)
Uses software decoding
video keeps pausing 25 fps, slightly pausing  

* Disclaimer: These values are estimates and are not official benchmark results.

Intel graphics features: hardware overlay

In many cases, the GPU composites all the layers in the webview for the Web graphics. On an Intel-based Chromebook, this is not true, because the hardware overlay has been supported since Sept. 2017. Let’s take a look at the difference.

 

Source: Images from this google doc

Legacy: GPU Composition

The following diagram shows how the GPU composites the UI of Chrome OS. As you can see, the GPU composites all the UI elements including web content and puts the final buffer into the primary plane.

Brand-new: Hardware Overlay

The following diagram shows how the Hardware overlay works. As you can see, the display compositor combines the overlay plane for a video and the primary plane for the UI/Web contents into a single frame buffer that is later scanned out for display. This method saves GPU bandwidth and battery power.

Add support for hardware overlay and atomic pageflip in Chrome OS

Hardware overlay is not only for video, but also for rendering Android applications that run on a hardware overlay plane, such as the Wayland client of Chrome OS. A WebGL overlay will be also supported in Gen 10. To do this, the display controller must support atomic updates to synchronize the plane updates. In M61 (released in Sept. 2017), atomic pageflip was enabled on Intel SoCs codenamed Kaby Lake and Apollo Lake.

Benefits of Ozone-gbm

Ozone-gbm has the following benefits:

  • Performance: Generally, zero-copy texture upload is 30~40% faster.
  • Memory consumption: When using zero-copy texture upload, the GPU process uses 65% less memory and the render process also uses 20% less memory.
  • UI responsiveness: Ozone-gbm aligns evdev and painting events with the GPU's Vsync signal to provide a better frame rate. This means you can handle input, layout, painting, compositing, rendering, and scanning within 16 ms. It reduces significant latency of touch and stylus.
  • Power saving: Saves more battery by using hardware features such as hardware overlay, hardware encode/decode, and zero-copy texture upload.

Upstream

The following Change Lists (CLs) have been submitted upstream to Chromium.

This CL enables the Intel i965 driver for mini-gbm, which allocates a buffer directly to GPU memory. The use_intel_minigbm build flag was added for this purpose. 

Allow to run ozone_demo on a Linux/Intel desktop 
First, we need to enable Intel driver by building Mesa 17.0.2 with --with-egl-platform=surfaceless --with-dri-drivers=i965 
BUG=733450 
TEST=ozone_demo 

$ cd ~/git/chromium/src 
$ gn gen out/Release "--args=use_ozone=true ozone_platform_gbm=true use_intel_minigbm=true" 
$ ninja -C out/Release ozone_demo 
$ export EGL_PLATFORM=surfaceless 
$ out/Release/ozone_demo

The second CL moves display related files ui/display/manager/chromeos to the parent directory. This was necessary because non-Chrome OS Linux also requires a display configurator, but it was only used for CrOS. This CL is already merged upstream. You can add the display configurator to your build by adding the build_display_configuration build flag to your project.

Separate display configurator from CrOS build 
This CL moves all files in ui/display/manager/chromeos to ui/display/manager and adds build_display_configuration GN arg 
so that the display configurator could be used in Linux desktop. 
BUG=733450

I have created a third CL that can run mus_demo, minimally implemented using mus (Mojo UI service). It runs with the UI service and Viz using Mojo.

Make mus_demo work on a desktop Linux 
This CL allows mus_demo to run on a desktop Linux by using Display Configurator that is only available to CrOS builds.
For this, DISPLAY_CONFIGURATION macro is added to enable Display Configurator when the build_display_configuration 
build flag is true. 
BUG=733450 
TEST=mash --service=mus_demo --enable-features=Mash 

$ cd ~/git/chromium/src 
$ gn gen out/Release "--args=use_ozone=true ozone_platform_gbm=true use_intel_minigbm=true build_display_configuration = true" 
$ ninja -C out/Release ozone_demo mash:all mus_demo 
$ export EGL_PLATFORM=surfaceless 
$ out/Release/mash --service=mus_demo --enable-features=Mash

VA-API video acceleration on a Linux desktop

A patch is in development that enables hardware accelerated video and image encoding/decoding on an Intel-based Linux desktop. The patch requires the libva/intel-vaapi-driver to be installed on the system path where the Chrome browser is executed. Once the patch is merged, video accelerations will be supported on a regular Linux desktop.

You can read more about the patch in this article.

How to enable ozone-gbm on Yocto* Linux

It was not easy to run ozone-gbm on a Linux desktop because you need to build your own Linux kernel and Mesa with patches. Instead, I tested ozone-gbm on Yocto Linux and shared the Yocto recipe on Github. You can test all the hardware acceleration features on Intel SoC using this recipe.

How to enable ozone-gbm on Arch Linux*

The following pictures show the ozone_demo (left) and mus_demo (right).

  

 

When you run ozone-gbm on Arch Linux, you do not need to modify the Linux Kernel and Mesa. Some patches have already landed so the ozone_demo works as-is. If you want to run the mus_demo, apply this patch

$ cd ~/git/chromium/src
$ gn gen out/Release "--args=use_ozone=true ozone_platform_gbm=true use_intel_minigbm=true build_display_configration=true"
$ ninja -C out/Release ozone_demo mash:all mus_demo
$ export EGL_PLATFORM=surfaceless
$ out/Release/ozone_demo --enable-drm-atomic --enable-overlay
$ out/Release/mash --service=mus_demo --enable-features=Mash

Demo video

I created the following Youtube* video that shows the performance difference between hardware acceleration and software fallback.

Future Plans

In Chromium M58, the Chromium browser worked on ozone-gbm. However, in Chromium M59 (and later), ozone-gbm functionality is broken on a Linux desktop. I plan to let content_shell or chromium run on ozone-gbm with the latest Chromium for a Linux desktop.

Special thanks to Dongseong Hwang, who originally implemented zero-copy texture upload and video hardware overlay, for his review.