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Historically, integrated graphics, with their notoriously lackluster performance, have been of little interest to power users. But perceptions began to change with Intel’s Sandy Bridge, and later its Ivy Bridge, microarchitecture. While Sandy Bridge’s DX10-class, Intel HD 2000/3000 graphics engines aren’t cutting-edge by any means, they offer enough performance for many mainstream PC users, and consequently, helped Intel gain market share in the graphics race. Ivy Bridge further improves the situation with a more powerful graphics core outfitted with additional execution units and DX11 support. Whereas Intel’s HD 3000 offers 12 EUs, Ivy Bridge’s HD 4000 engine has 16.
But perhaps the most sought-after feature of Sandy Bridge and Ivy Bridge is Quick Sync. Quick Sync is a dedicated encoding/decoding engine that can burn through video-encoding tasks lightning-fast. Problem is, Quick Sync is part of the GPU block on Sandy Bridge and Ivy Bridge processors, and when a discrete GPU is installed and no monitor is connected to the integrated GPU, Quick Sync is unavailable.
Not being able to use Quick Sync and discrete graphics simultaneously didn’t sit well with enthusiasts, but a workable solution was made available when LucidLogix introduced Virtu, a product that can virtualize the GPUs in systems and enabled hybrid graphics configurations. With Virtu, users can enjoy the benefits of a discrete GPU when gaming and still leverage an integrated GPU for power savings or Quick Sync. The best part is that Virtu is supported by a variety of motherboards. On the following pages we’re going to explain how Virtu works and how you can set it up on your own system, and then we’ll show you how a hybrid graphics configuration affected benchmark performance on our test systems.
Although the underlying technology is relatively complex, it’s somewhat easy to explain and understand how Virtu works. First and foremost, note that Virtu is a software solution from top to bottom—save for programming some BIOS code, no modifications are necessary at the hardware level. Virtu requires special hooks in the BIOS and the presence of both discrete (dGPU) and processor/integrated (iGPU) graphics in a system, but that’s it.
When Virtu is installed on a system, it essentially virtualizes the available GPUs. The name Virtu is actually an abbreviation of GPU Virtualization. With Virtu, Lucid’s Multi‑GPU Abstraction Layer is installed between the OS and drivers, and that abstraction layer intercepts DirectX API calls from games or applications. At this point in time, OpenGL and
WebGL are not supported. Once a call is intercepted, Virtu’s Rendering Assignment Manager then analyzes it and decides to shuttle the subsequent task to either the iGPU or dGPU, based on a set of predetermined application profiles, which includes hundreds of games and multimedia tools.
Virtu can be configured in two modes: i-Mode or d-Mode. I-Mode refers to a configuration in which a monitor is connected to the integrated graphics engine’s display output, while d-Mode means the monitor is connected to the discrete GPU. We mention the modes available because the final step Virtu performs is dependent on the mode being used. Once a task is complete, the output (typically a rendered frame) is copied to the appropriate GPU’s frame buffer, where it is finally output to the screen. When operating in i-Mode, the dGPU’s output is copied to the iGPU’s frame buffer memory; vice versa for d-Mode.
Currently there are three different versions of LucidLogix Virtu available to end users: Virtu Green, Virtu Universal, and Virtu MVP. All the different versions function in a similar manner, but each has a different feature set. Virtu Green is the most basic version and works only on Intel platforms. Next up the chain is Virtu Universal, which works with both Intel and AMD platforms and also adds support for Lucid’s Virtual V-Sync technology. Finally, there is Virtu MVP, which has all the features and compatibility of Universal, but adds support for Lucid’s HyperFormance technology, as well.
While they’re independently configurable, Virtual V-Sync and HyperFormance are interconnected. These two features have been mistakenly characterized as game performance enhancers, when in fact they’ll only affect image quality and input responsiveness. Virtual V-Sync leverages the iGPU’s resources when the discrete GPU is being used to probe the dGPU’s frame buffer and ensure that only the last fully rendered frame is shown on the screen. By doing so, Virtual V-Sync prevents tearing artifacts and always ensures the latest frame data is displayed on screen. It’s only useful, however, when a game’s frame rate exceeds the refresh rate of the attached monitor, which is usually 60Hz (or 60fps) for mainstream LCDs. HyperFormance uses a predictive algorithm to ascertain which frames will never be displayed, and removes any unnecessary rendering tasks for those frames from the pipeline, freeing up the dGPU to process only the items which will ultimately be displayed. This results in a decreased workload for the dGPU and an increase in responsiveness, but like Virtual V-Sync, HyperFormance is only useful when frame rates exceed the monitor’s refresh rate.
Short of having a compatible motherboard, as well as discrete and integrated processor GPUs, there are no specific hardware considerations for Virtu. As we’ve mentioned, it’s a software-only solution. LucidLogix has been working with motherboard manufacturers to have Virtu included with strategic motherboards—typically those supporting Intel’s Sandy Bridge and Ivy Bridge-based processors—but Virtu is also compatible with AMD’s A-Series APU chipsets. Due to Virtu’s requirement for both discrete and integrated graphics processors, however, it does not support any high-end, enthusiast‑class chipsets, like those designed for Intel’s Sandy Bridge-E or AMD’s Bulldozer, for example, as those processors lack on-die graphics.
At this point in time, Virtu is qualified to work with single discrete-GPU configurations and is also compatible with any display output—DVI, DisplayPort, HDMI, etc. are all supported. Virtu also supports multimonitor configurations, but multi-GPU support is iffy. We asked Lucid about Virtu’s support for CrossFire or SLI multi-GPU configs and were told, “The reason for limited support today is our flexibility to plug the display in i-Mode (to motherboard) or d-Mode (discrete GPU). In i-Mode, which is the most popular one, we enable additional power savings and noise reduction, but the vendor control panels for SLI or CrossFire are not available. Also, the Virtu product line is shipped in mass volumes (expecting to pass 10 million units by end of year). Virtu is for the mass market. SLI/CF are relatively smaller markets and require a great deal of work with special workarounds.” Indeed, when in i-Mode, Nvidia’s and AMD’s driver control panels will not load. In fact, if you try to access it when Virtu is enabled in i-Mode, an error message will pop up saying a supported GPU is not available, although the drivers for the GPU do load with Windows. The nonfunctioning control panels prevent users from switching on SLI or CrossFire, though, and prevent their application profiles from properly detecting games. With that said, you can start up a system in d-Mode, turn on SLI or CrossFire, then switch back to i-Mode, but success isn’t guaranteed. We did get CrossFire working in i-Mode, but SLI never scaled properly.