Most of the CPU usage on an RD Session Host system is driven by applications. Desktop applications are usually optimized toward responsiveness with the goal of minimizing how long it takes an application to respond to a user request. However, in a server environment it is equally important to minimize the total amount of CPU that is used to complete an action to avoid adversely affecting other sessions.
Consider the following suggestions when you configure applications to be used on an RD Session Host system:
Minimize background/Idle loop processing.
Typical examples are disabling background grammar/spell checking, data indexing for search, and background saves.
Minimize how often an application polls to do a state check or update.
Disabling such behaviors or increasing the interval between polling iterations and timer firing significantly benefits CPU usage because the CPU effect of such activities is quickly amplified for many active sessions. Typical examples are connection status icons and status bar information updates.
Minimize resource contention between applications by reducing their synchronization frequency with that resource.
Examples of such resources include registry keys and configuration files. Examples of such application components and features are status indicator (like shell notifications), background indexing or change monitoring, and offline synchronization.
Disable unnecessary processes that are registered to be started at user logon or session startup.
These processes can significantly contribute to the CPU cost of creating a new session for the user, which generally is a CPU-intensive process and can be very expensive in morning scenarios. Use MsConfig.exe or MsInfo32.exe to obtain a list of processes that are started at user logon.
When possible, avoid multimedia application components for RD Session Host deployments.
Video playback causes high bandwidth usage for the RD Session Host connection, and audio playback causes high bandwidth usage on the audio redirection channel. Also, multimedia processing (encoding and decoding, mixing, and so on) has a significant CPU usage cost.
For memory consumption, consider the following suggestions:
Verify that DLLs that applications load are not relocated at load.
If DLLs are relocated, it is impossible to share their code across sessions, which significantly increases the footprint of a session. This is one of the most common memory-related performance problems in RD Session Host.
For common language runtime (CLR) applications, use Native Image Generator (Ngen.exe) to increase page sharing and reduce CPU overhead.
When possible, apply similar techniques to other similar execution engines.
Remote Desktop Session Host Tuning Parameters
Insufficient pagefile size can cause memory allocation failures either in applications or system components. A general guideline is that the combined size of the pagefiles should be two to three times larger than the physical memory size. You can use the Memory\Committed Bytes performance counter to monitor how much committed virtual memory is on the system. When the value of this counter reaches close to the total combined size of physical memory and pagefiles, memory allocation begins to fail. Because of significant disk I/O activity that pagefile access generates, consider using a dedicated storage device for the pagefile, ideally a high-performance one such as a striped RAID array.
For more specific storage tuning guidelines, see “Performance Tuning for the Storage Subsystem” earlier in this guide.
Antivirus and Antispyware
Installing antivirus and antispyware software on an RD Session Host server greatly affects overall system performance, especially CPU usage. We highly recommend that you exclude from the active monitoring list all the folders that hold temporary files, especially those that services and other system components generate.
Task Scheduler (which can be accessed under All Programs > Accessories > System Tools) lets you examine the list of tasks that are scheduled for different events. For RD Session Host, it is useful to focus specifically on the tasks that are configured to run on idle, at user logon, or on session connect and disconnect. Because of the specifics of the deployment, many of these tasks might be unnecessary.
Desktop Notification Icons
Notification icons on the desktop can have fairly expensive refreshing mechanisms. You can use Customize Notifications Icons to examine the list of notifications that are available in the system. Generally, it is best to disable unnecessary notifications by either removing the component that registers them from the startup list or by changing the configuration on applications and system components to disable them.
You can implement the following tuning parameters by opening the MMC snap-in for Group Policy (Gpedit.smc) and making the respective changes under Computer Configuration > Administrative Templates > Windows Components > Remote Desktop Services:
Color depth can be adjusted under Remote Session Environment > Limit Maximum Color Depth with possible values of 8, 15, 16, and 32 bit. The default value is 16 bit, and increasing the bit depth increases memory and bandwidth consumption. Or, the color depth can be adjusted from TSConfig.exe by opening the Properties dialog box for a specific connection and, on the Client Setting tab, changing the selected value in the drop-down box under Color Depth. The Limit Maximum Color Depth check box must be selected.
Remote Desktop Protocol compression.
Remote Desktop Protocol (RDP) compression can be configured under Remote Session Environment > Set compression algorithm for RDP data. Three values are possible:
Optimized to use less memory is the configuration that matches the default Windows Server 2003 configuration. This uses the least amount of memory per session but has the lowest compression ratio and therefore the highest bandwidth consumption.
Balances memory and network bandwidth is the default setting for Windows Server 2008 R2. This has reduced bandwidth consumption while marginally increasing memory consumption (approximately 200 KB per session).
Optimized to use less network bandwidth further reduces network bandwidth usage at a cost of approximately 2 MB per session. This memory is allocated in the kernel virtual address space and can have a significant effect on 32-bit processor–based systems that are running a fairly large number of users. Because 64-bit systems do not have these issues, this setting is recommended if the additional memory cost is considered acceptable. If you want to use this setting, you should assess the maximum number of sessions and test to that level with this setting before placing a server in production.
Device redirection can be configured under Device and Resource Redirection. Or, it can be configured through Remote Desktop Session Host Configuration by opening the properties for a specific connection such as RDP-Tcp and, on the Client Settings tab, changing Redirection settings.
Generally, device redirection increases how much network bandwidth RD Session Host connections use because data is exchanged between devices on the client machines and processes that are running in the server session. The extent of the increase is a function of the frequency of operations that are performed by the applications that are running on the server against the redirected devices.
Printer redirection and Plug and Play device redirection also increase logon CPU usage. You can redirect printers in two ways:
Matching printer driver-based redirection when a driver for the printer must be installed on the server. Earlier releases of Windows Server used this method.
Easy Print printer driver redirection, introduced in Windows Server 2008, uses a common printer driver for all printers.
We recommend the Easy Print method because it causes less CPU usage for printer installation at connection time. The matching driver method causes increased CPU usage because it requires the spooler service to load different drivers. For bandwidth usage, the Easy Print method causes slightly increased network bandwidth usage, but not significant enough to offset the other performance, manageability, and reliability benefits.
Audio redirection is disabled by default because using it causes a steady stream of network traffic. Audio redirection also enables users to run multimedia applications that typically have high CPU consumption.
Client Experience Settings
The Remote Desktop Connection (RDC) Client provides control over a range of settings that influence network bandwidth performance for the Remote Desktop Services (RDS) connection. You can access them either through the RDC Client user interface on the Experience tab or as settings in the RDP file:
Disable wallpaper (RDP file setting: disable wallpaper:i:0) suppresses the display of desktop wallpaper on redirected connections. It can significantly reduce bandwidth usage if desktop wallpaper consists of an image or other content with significant drawing cost.
Font smoothing (RDP file setting: allow font smoothing:i:0) controls ClearType font rendering support. Although this improves the rendering quality for fonts when it is enabled, it does affect network bandwidth consumption significantly.
Desktop composition is supported only for a remote session to Windows Vista and has no relevance for server systems.
Show contents of windows while dragging (RDP file setting: disable full window drag:i:1), when it is disabled, reduces bandwidth by displaying only the window frame instead of all the contents when dragged.
Menu and window animation (represented by two distinct RDP file settings: disable menu anims:i:1 and disable cursor setting:i:1), when it is disabled, reduces bandwidth by disabling animation on menus (such as fading) and cursors.
Visual styles (RDP file setting: disable themes:i:1), when it is disabled, reduces bandwidth by simplifying theme drawings that use the classic theme.
Bitmap cache (RDP file setting: bitmapcachepersistenable:i:1), when it is enabled, creates a client-side cache of bitmaps that are rendered in the session. It is a significant improvement on bandwidth usage and should always be enabled (except for security considerations).
Using the Experience tab within the Remote Desktop Connection Client you can choose your connection speed to influence network bandwidth performance. The following list indicates which options are chosen if you change the connection speed within the Experience tab of the Remote Desktop Connection Client:
Desktop composition; show contents of windows while dragging; menu and window animation; persistent bitmap caching; visual styles; desktop background
WAN (10 Mbps or higher with high latency)
Desktop composition; show contents of windows while dragging; menu and window animation; persistent bitmap caching; visual styles; desktop background (all)
LAN (10 Mbps or higher)
Desktop composition; show contents of windows while dragging; menu and window animation; persistent bitmap caching; themes; desktop background
When the RDP connection profile is saved, it creates an xxx.rdp file where xxx is the friendly name chosen by the user (the default is default.rdp). The speed optimization settings in the xxx.rdp configuration file are attributed as follows:
Cellular with latency=3
WAN with latency=5
Desktop size for remote sessions can be controlled either through the RDC client user interface (on the Display tab under Remote desktop size settings) or the RDP file (desktopwidth:i:1152 and desktopheight:i:864). The larger the desktop size, the greater the memory and bandwidth consumption that is associated with that session. The current maximum desktop size that a server accepts is 4096 x 2048.