Linux Virtual Delivery Agent

Graphics configuration and fine-tuning

This article provides guidance for the Linux VDA graphics configuration and fine-tuning.

For more information, see System requirements and the Installation overview section.

Configuration

Video codec for compression

Thinwire is the display remoting technology used in the Linux VDA. The technology allows graphics generated on one machine to be transmitted, typically across a network, to another machine for display.

The Use video codec for compression graphics policy sets the default graphics mode and provides the following options for different use cases:

  • Use when preferred. This setting is the default. No additional configuration is required. It ensures that Thinwire is selected for all Citrix connections, and optimized for scalability, bandwidth, and superior image quality for typical desktop workloads.
  • For the entire screen. Delivers Thinwire with full-screen H.264 or H.265 to optimize for improved user experience and bandwidth, especially in cases with heavy use of 3D graphics.
  • For actively changing regions. The adaptive display technology in Thinwire identifies moving images (video, 3D in motion). It uses H.264 only in the part of the screen where the image is moving. The Selective use of the H.264 video codec enables HDX Thinwire to detect and encode parts of the screen that are frequently updated using the H.264 video codec. Still image compression (JPEG, RLE) and bitmap caching continue to be used for the rest of the screen, including text and photographic imagery. Users get the benefit of lower bandwidth consumption and better quality for video content combined with lossless text or high quality imagery elsewhere. To enable this feature, set the Use video codec for compression policy to Use when preferred (default) or For actively changing regions. For more information, see Graphics policy settings. To enable H.264 hardware encoding for this feature, see H.264 hardware encoding.

    For the entire screen being selected

Some other policy settings, including the following visual display policy settings can be used to fine-tune the performance of display remoting:

H.264 hardware encoding

The Use hardware encoding for video codec policy allows the use of graphics hardware, if available, to compress screen elements with the video codec. If such hardware is not available, the VDA falls back to CPU-based encoding using the software video codec.

Starting with version 2204, the Linux VDA supports selective use of the H.264 hardware codec for actively changing regions. This feature offloads CPU video compression consumption to hardware and improves image quality and the number of frames per second (FPS). To enable the feature, do the following:

  1. Enable the Use hardware encoding for video codec policy.

  2. Enable the Use video codec for compression policy and select For actively changing regions.

Allow visually lossless compression

The Allow visually lossless compression policy allows visually lossless compression to be used instead of true lossless compression for graphics. Visually lossless improves performance over true lossless, but has minor loss that is unnoticeable by sight. This setting changes the way the values of the Visual quality setting are used.

The Allow visually lossless compression policy is disabled by default. To enable visually lossless compression, set Allow visually lossless compression to Enabled and the Visual quality policy to Build to Lossless.

If the Use video codec for compression policy is set to Do not use video codec, visually lossless compression applies to static image encoding. If the Use video codec for compression policy is set to a graphics mode other than Do not use video codec, visually lossless compression applies to H.264 encoding.

The following clients support Selective H.264:

  • Citrix Receiver for Windows 4.9 through 4.12
  • Citrix Receiver for Linux 13.5 through 13.10
  • Citrix Workspace app 1808 for Windows and later
  • Citrix Workspace app 1808 for Linux and later

For more information about the Visual quality and Use video codec for compression policy settings, see Visual display policy settings and Graphics policy settings.

Support for H.265 video codec

Starting with the 7.18 release, the Linux VDA supports the H.265 video codec for hardware acceleration of remote graphics and videos.

You can use this feature on:

  • Citrix Receiver for Windows 4.10 through 4.12
  • Citrix Workspace app 1808 for Windows and later

To benefit from this feature, enable it on both the Linux VDA and on your client. If the GPU of your client doesn’t support H.265 decoding using the DXVA interface, the H.265 Decoding for graphics policy setting is ignored and sessions fall back to using the H.264 video codec. For more information, see H.265 video encoding.

To enable H.265 hardware encoding on the VDA:

  1. Enable the Use hardware encoding for video codec policy.
  2. Enable the Optimize for 3D graphics workload policy
  3. Ensure that the Use video codec for compression policy is default or set to For the entire screen.
  4. Ensure that the Visual quality policy is NOT set to Build to Lossless or Always Lossless.

To enable H.265 hardware encoding on your client, see H.265 video encoding.

Support for YUV444 software encoding

The Linux VDA supports YUV444 software encoding. The YUV encoding scheme assigns both brightness and color values to each pixel. In YUV, ‘Y’ represents the brightness or ‘luma’ value, and ‘UV’ represents the color or ‘chroma’ values. You can use this feature on Citrix Receiver for Windows 4.10 through 4.12 and on Citrix Workspace app 1808 for Windows and later.

Each unique Y, U, or V value comprises 8 bits, or one byte, of data. The YUV444 data format transmits 24 bits per pixel. The YUV422 data format shares U and V values between two pixels, which results in an average transmission rate of 16 bits per pixel. The following table shows an intuitive comparison between YUV444 and YUV420.

YUV444 YUV420
YUV444 YUV420

To enable YUV444 software encoding on the VDA:

  1. Enable the Allow visually lossless compression policy.
  2. Ensure that the Use video codec for compression policy is set to For the entire screen.
  3. Ensure that the Visual quality policy is set to Always Lossless or Build to Lossless.

Graphics quality slider

We have included a graphics quality slider in the graphics status indicator tool that runs in your virtual Linux sessions. The slider helps to find the right balance between image quality and interactivity.

To use the slider, complete the following steps:

  1. Enable the Graphic status indicator policy in Citrix Studio.

    The Graphic status indicator policy

  2. Open the Terminal and run the ctxslider command. The slider UI appears.

    Note:

    If you have set the Visual Quality policy to Always Lossless or Build to Lossless, the slider UI is not showing.

    Graphic quality slider

    The following choices are now available:

    • To change the image quality, move the slider. The slider supports a range of 0–9.
    • To use system-defined settings, select Let the system decide.
    • To switch to lossless mode, select Pixel perfect.

Adjust average bit rates based on bandwidth estimates

Citrix enhances HDX 3D Pro hardware encoding by adjusting average bit rates based on bandwidth estimates.

When HDX 3D Pro hardware encoding is in use, the VDA can intermittently estimate the bandwidth of the network and adjust the bit rates of encoded frames accordingly. This new feature provides a mechanism to balance between sharpness and fluency.

This feature is enabled by default. To disable it, run the following command:

sudo /opt/Citrix/VDA/bin/ctxreg create -k "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Citrix\Thinwire" -t "REG_DWORD" -v "DisableReconfigureEncoder" -d "0x00000001" --force
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In addition to using this feature, you can also run the following commands to adjust between sharpness and fluency. The AverageBitRatePercent and MaxBitRatePercent parameters set the percentage of bandwidth usage. The higher values you set, the sharper graphics and lower fluency you get. The recommended setting range is 50–100.

sudo /opt/Citrix/VDA/bin/ctxreg create -k "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Citrix\Thinwire" -t "REG_DWORD" -v "AverageBitRatePercent" -d "90" --force

sudo /opt/Citrix/VDA/bin/ctxreg create -k "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Citrix\Thinwire" -t "REG_DWORD" -v "MaxBitRatePercent" -d "100" --force
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In the average bit rate adjustment, when your screen holds still, the most recent frame stays in a low-quality state because no new frames are sent. Sharpening support can address this issue by reconfiguring and immediately sending the most recent frame at the highest quality.

For a full list of the policies supported by the Linux VDA Thinwire, see Policy support list.

For information on the configuration of multi-monitor support on the Linux VDA, see CTX220128.

Parallel processing

Thinwire can improve the number of Frames Per Second (FPS) by parallelizing certain tasks, with the overhead of slightly higher overall CPU consumption. This feature is disabled by default. To enable the feature, run the following command on your VDA:

sudo /opt/Citrix/VDA/bin/ctxreg create -k "HKLM\System\CurrentControlSet\Control\Citrix\Thinwire" -t "REG_DWORD" -v "ParallelProcessing" -d "0x00000001" --force
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Troubleshooting

Check which graphics mode is in use

Run the following command to check which graphics mode is in use (0 means TW+. 1 means full-screen video codec):

sudo /opt/Citrix/VDA/bin/ctxreg dump | grep GraphicsMode
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The result resembles:

create -k "HKLM\Software\Citrix\Ica\Session\4\Graphics" -t "REG_DWORD" -v "GraphicsMode" -d "0x00000000" --force

Check whether H.264 is in use

Run the following command to check whether H.264 is in use (0 means not in use. 1 means in use):

sudo /opt/Citrix/VDA/bin/ctxreg dump | grep H264
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The result resembles:

create -k "HKLM\Software\Citrix\Ica\Session\4\Graphics" -t "REG_DWORD" -v "H264" -d "0x00000000" --force

Check whether H.265 is in use

Run the following command to check whether full-screen H.265 is in use (0 means not in use. 1 means in use):

sudo /opt/Citrix/VDA/bin/ctxreg dump | grep H265
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The result resembles:

create -k "HKLM\Software\Citrix\Ica\Session\4\Graphics" -t "REG_DWORD" -v "H265" -d "0x00000000" --force

Check which YUV encoding scheme is in use

Run the following command to check which YUV encoding scheme is in use (0 means YUV420. 1 means YUV422. 2 means YUV444):

Note: The value of YUVFormat is meaningful only when a video codec is in use.

sudo /opt/Citrix/VDA/bin/ctxreg dump | grep YUVFormat
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The result resembles:

create -k "HKLM\Software\Citrix\Ica\Session\4\Graphics" -t "REG_DWORD" -v "YUVFormat" -d "0x00000000" --force

Check whether YUV444 software encoding is in use

Run the following command to check whether YUV444 software encoding is in use:

sudo /opt/Citrix/VDA/bin/ctxreg dump | grep Graphics
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When YUV444 is in use, the result resembles:

create -k "HKLM\Software\Citrix\Ica\Session\4\Graphics" -t "REG_DWORD" -v "GraphicsMode" -d "0x00000001" --force
create -k "HKLM\Software\Citrix\Ica\Session\4\Graphics" -t "REG_DWORD" -v "H264" -d "0x00000001" --force
create -k "HKLM\Software\Citrix\Ica\Session\4\Graphics" -t "REG_DWORD" -v "HardwareEncoding" -d "0x00000000" --force
create -k "HKLM\Software\Citrix\Ica\Session\4\Graphics" -t "REG_DWORD" -v "YUVFormat" -d "0x00000002" --force

Check whether hardware encoding is in use for 3D Pro

Run the following command (0 means not in use. 1 means in use):

sudo /opt/Citrix/VDA/bin/ctxreg dump | grep HardwareEncoding
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The results resemble:

create -k "HKLM\Software\Citrix\Ica\Session\1\Graphics" -t "REG_DWORD" -v "HardwareEncoding" -d "0x00000001" --force

Another way is to use the nvidia-smi command. The outputs resemble the following if hardware encoding is in use:

Tue Apr 12 10:42:03 2016
+------------------------------------------------------+
| NVIDIA-SMI 361.28     Driver Version: 361.28         |
|-------------------------------+----------------------+----------------------+
| GPU  Name        Persistence-M| Bus-Id        Disp.A | Volatile Uncorr. ECC |
| Fan  Temp  Perf  Pwr:Usage/Cap|         Memory-Usage | GPU-Util  Compute M. |
|===============================+======================+======================|
|   0  GRID K1             Off  | 0000:00:05.0     Off |                  N/A |
| N/A   42C    P0    14W /  31W |    207MiB /  4095MiB |      8%      Default |
+-------------------------------+----------------------+----------------------+

+-----------------------------------------------------------------------------+
| Processes:                                                       GPU Memory |
|  GPU       PID  Type  Process name                               Usage      |
|=============================================================================|
|    0      2164  C+G   /usr/local/bin/ctxgfx                          106MiB |
|    0      2187    G   Xorg                                            85MiB |
+-----------------------------------------------------------------------------+
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Verify that the NVIDIA GRID graphics driver is installed correctly

To verify that the NVIDIA GRID graphics driver is installed correctly, run nvidia-smi. The results resemble:

+------------------------------------------------------+
| NVIDIA-SMI 352.70     Driver Version: 352.70         |
|-------------------------------+----------------------+----------------------+
| GPU  Name        Persistence-M| Bus-Id        Disp.A | Volatile Uncorr. ECC |
| Fan  Temp  Perf  Pwr:Usage/Cap|         Memory-Usage | GPU-Util  Compute M. |
|===============================+======================+======================|
|   0  Tesla M60           Off  | 0000:00:05.0     Off |                  Off |
| N/A   20C    P0    37W / 150W |     19MiB /  8191MiB |      0%      Default |
+-------------------------------+----------------------+----------------------+

+-----------------------------------------------------------------------------+
| Processes:                                                       GPU Memory |
|  GPU       PID  Type  Process name                               Usage      |
|=============================================================================|
|  No running processes found                                                 |
+-----------------------------------------------------------------------------+
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Set the correct configuration for the card:

etc/X11/ctx-nvidia.sh

HDX 3D Pro multi-monitor redraw issues

If you are seeing redraw issues on screens other than the primary monitor, check that the NVIDIA GRID license is available.

Check Xorg error logs

The log file of Xorg is named similar to Xorg.{DISPLAY}.log in the /var/log/ folder.

Known issues and limitations

For vGPU, the Citrix Hypervisor local console shows the ICA desktop session screen

Workaround: Disable the VM’s local VGA console by running the following commands:

For Citrix Hypervisor 8.1 and later:

[root@xenserver ~]# xe vgpu-param-set uuid=vgpu-uuid extra_args=disable_vnc=1
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For Citrix Hypervisor earlier than 8.1:

xe vm-param-set uuid=<vm-uuid> platform:vgpu_extra_args="disable_vnc=1"
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NVIDIA K2 graphics cards do not support YUV444 hardware encoding in pass-through mode

With Build to Lossless enabled through the policy setting, a black or gray screen appears when users are launching an app/desktop session with an NVIDIA K2 graphics card. The issue occurs because NVIDIA K2 graphics cards do not support YUV444 hardware encoding in pass-through mode. For more information, see Video Encode and Decode GPU Support Matrix.

Gnome 3 desktop popups slow when logging on

It is a limitation of Gnome 3 desktop session startup.

Some OpenGL/WebGL applications do not render well upon resizing the Citrix Workspace app window

Resizing the window of Citrix Workspace app changes the screen resolution. The NVIDIA proprietary driver changes some internal states and might require applications to respond accordingly. For example, the WebGL library element lightgl.js might spawn an error saying that ‘Rendering to this texture is not supported (incomplete frame buffer)’.

Graphics configuration and fine-tuning