Throughout the life of XenApp and XenDesktop, the combination of many factors such as the architecture of the base operating system, graphics device drivers and network bandwidth have been a determining factor in the overall end-user experience from a graphics quality standpoint. Citrix’s HDX protocol has made many enhancements in this area using such technologies as advanced compression methods and features such as Progressive Display and Adaptive Display. In addition, many HDX features (for example HDX MediaStream, HDX RichGraphics, HDX Optimization Pack for Google Earth) are provided to enhance the experience with certain types of content by offloading certain processes onto the client endpoint when possible.
However, because of limitations in current technologies, many Citrix environments do hit certain points where customers must make some amount of trade-off between end user-experience and session performance. The most prevalent example of this is improving session performance over lower bandwidth/WAN connections by reducing graphics quality using image compression. As Citrix continues to make further innovations in this area, there are some features added within the existing product versions that are often overlooked or misconfigured that can greatly improve current graphics related performance in certain environments. For example, some settings within an environment can be tweaked to try and avoid screen refresh issues sometimes seen with certain types of applications, or with scrolling issues that have also been reported amongst customers in the past. This article serves to point out some of these overlooked or misconfigured settings.
Introduced in XenDesktop 5.5 and HRP01 for XenApp 6.5, the Adaptive Display feature is the evolution of the Progressive Display feature introduced in previous versions. It is comprised of multiple Citrix policies that tune various graphics settings in relation to an available bandwidth to always provide the most optimal end-user experience. With this, the customers need not worry about creating different settings or policies for different groups of people depending on those user’s profiles (for example. geographic location, applications most used.). Adaptive display is enabled by default but you must ensure that Progressive Display (the “Progressive compression level” policy) is not enabled so that Adaptive Display kicks in.
- The following is a good third party blog on the different policies involved in Adaptive Display and how they can and should be tweaked if desired http://bramwolfs.com/2012/05/08/adaptive-display-whats-in-the-game-and-do-we-need-to-fine-tune/.
ForceLVBMode and DeferredUpdateMode
The ForceLVBMode and DeferredUpdateMode settings on the Citrix Receiver were created to address screen repaint issues because of poor refresh rate. Although many screen refresh issues can be specific to the actual design of the application being used, these settings can help to improve screen refresh and scrolling performance for scenarios such as pass-through sessions and multi-monitor sessions.
Applications that use Off-Screen Surfaces (OSS) might exhibit unexpected behaviors (for example screen flickering and issues with colors). The performance of such applications running within Citrix sessions depends largely on the design of the application and the underlying operating system. Therefore, certain applications might perform better in a virtualized environment by drawing graphics directly to the screen rather than using OSS for caching bitmaps. For example, we have seen flickering issues with Internet Explorer 8 running inside of a Windows 7 XenDesktop session when OSS is enabled. However, at the same time, Internet Explorer 9 does not appear to have the same issue when used in the same scenario. OSS does provide some bandwidth saving. However, disabling it does not introduce any risk for LAN or WAN connected session. Hence the fact that an optional server side setting has also been added in the latest versions of XenApp and XenDesktop to disable OSS.
- eDocs – EnableOSS ICA Setting
Read the entire article here at the Citrix Knowledgebase.