Differences between Vista and Seven video card implementation

[Modelworks]

I know there has been a lot of people wondering what is the difference in vista and windows 7 in the video card usage department. Well here is the details on what is different in the two regarding desktop usage.


The full blog is here:
http://blogs.msdn.com/e7/

GDI Concurrency

A number of performance traces we investigated in the context of desktop responsiveness pointed us to the design of a key synchronization mechanism in GDI. The performance challenge happens because the design of GDI in Windows Vista allows only a single application to hold a system-wide exclusive global lock. While this seems obvious in hindsight, when this decision was originally made the performance characteristics of different parts of the system made this optimistic implementation perfectly reasonable.

GDI applications running simultaneously vie for this global lock in order to render on the screen. The application that accesses the global lock prevents other applications from rendering till it releases the global lock. The situation often gets exacerbated when the application that is holding the lock needs to page in a large amount of memory from the disk since moving the memory from the disk to RAM takes a relatively long time.

The solution to the problem was therefore to reduce the lock contention and improve concurrency by re-architecting the internal synchronization mechanism through which multiple applications can reliably render at the same time. Contention due to the global exclusive lock is avoided by implementing a number of fine-grained locks which are not exclusive but aid parallelism. The increased number of fine-grained locks adds a small overhead for scenarios where only a single application is rendering at a time.

Special attention was paid to GDI application compatibility as changing internal synchronization mechanism in the most widely used API stack could potentially give rise to timing issues such as deadlocks and rendering corruption.

This work also resulted in better rendering performance of concurrent GDI applications on multi-core CPUs. Multi-core Windows PCs benefit from these changes as more than one application can now be rendering at the same time.

After the GDI concurrency work was implemented in the Windows 7 builds leading to the Beta, we saw a large reduction in the number of desktop responsiveness issues reported by our testers which were caused by one application blocking another one due to GDI. To further validate the scalability of our new implementation, we wrote tests that draw 2D GDI primitives and measured the rendering throughput by launching simultaneously multiple such applications. The throughput is measured by adding together the frame rate (FPS) of each application window. Below is a sample of these results on a quad-core CPU system.

Without the Windows 7 GDI concurrency, the rendering throughput of these applications is effectively limited to the performance of a single CPU core. Since only a single application can acquire the global exclusive lock while the others are waiting, this scenario doesn?t benefit from multiple CPU cores. This demonstrates that GDI applications in Windows 7 are now much less dependent on one another. This benefit will not need any new display drivers; it will work on any Vista (WDDM 1.0) and newer display drivers.

In Windows Vista, the amount of memory required to run multiple windows scales linearly with the number of windows opened on the system. This results in more memory pressure when there are more windows or if the monitors have higher resolution. It gets worse if you have more than one monitor. As part of investigating various means to improve system responsiveness, we saw a great opportunity in reducing the usage of system memory by DWM.

In Windows Vista, every GDI application window accounts for two memory allocations which hold identical content ? one in video memory and one in system memory. DWM is responsible for composition of the desktop through the graphics hardware. Hence, it requires a copy of the same allocation in video memory, which is easily accessible by the graphics hardware.

The duplicate copy present in system memory is required because GDI is being rendered utilizing the CPU completely in the operating system without any assistance or ?acceleration? by the graphics hardware. As the CPU performs all the tasks for rendering GDI applications, it requires an easily accessible cacheable copy of memory.

Windows 7 saves one copy of the memory allocation per application window by getting rid of the system memory copy entirely. Thus, for a GDI application window visible on the desktop, the memory consumed is cut in half.

Based on real-world application statistics, a tiny snapshot of which is seen above, we worked with our graphics IHV partners to provide support in their drivers to accelerate the most commonly used GDI operations. Windows 7 systems with these updated drivers, called ?WDDM v1.1? will thus benefit from this memory savings work. Please note that WDDM 1.0 drivers continue to function and are fully supported on Windows 7. You might have seen Windows Update providing these 1.1 drivers during the Beta?these drivers are themselves in Beta.

For Windows 7, we have worked closely with our Graphics IHV partners, helping them improve the WDDM drivers? gaming performance with specific changes to how Windows 7 works under the hood, while maintaining the same driver model and compatibility. Our continued investments in performance tools has helped us and our IHV partners track down and analyze various gaming performance bottlenecks and fix them in subsequent driver releases. The fundamentals of the Windows Display Driver Model remain unchanged in Windows 7. Some policies around GPU scheduling and memory management were changed to enable better performance in certain scenarios.

Because these benchmarks are very sensitive to the specific hardware, firmware, drivers, and overall system and because these are so widely measured and discussed elsewhere we are going to leave these comparisons to third parties. Like many areas in Windows 7, our commitment is to engineer even better performance across many dimensions. We believe it is better for you to experience these efforts directly. In comparing Windows 7, we would encourage the comparison using Windows Vista SP1 and keep in mind the difference you might see in WDDM 1.0 v. 1.1 and that the 1.1 drivers are still under development.

 

[BD2003]

Windows 7 saves one copy of the memory allocation per application window by getting rid of the system memory copy entirely. Thus, for a GDI application window visible on the desktop, the memory consumed is cut in half.

This is the most important part, and why windows 7 seems to run much better than vista on low memory systems.

Especially when youre dealing with integrated graphics that used shared memory, which is usually found in systems with already limited memory...this helps a ton.

 

[Fox5]

So they're speeding up 2D graphics and cutting down on system memory usage...
Well nice upgrades I suppose, but not enough to get me to buy another new OS. Ram is cheaper than Windows, and I can already have 50+ windows open with no lag.

 

[bsobel]

Originally posted by: Fox5
So they're speeding up 2D graphics and cutting down on system memory usage...
Well nice upgrades I suppose, but not enough to get me to buy another new OS. Ram is cheaper than Windows, and I can already have 50+ windows open with no lag.

So the OP posts about a specific driver model change in W7 and you extrapolate that to it being the only change in the OS?

 

[VirtualLarry]

It should also be noted in this thread that one of the major new features of WDDM 1.1, is heterogenous video drives, like in XP, but not in Vista. That means that you can install both NV and ATI cards into the same machine, and they will work together. (ATI for gfx, NV for physx, etc.)

 

[Modelworks]

Originally posted by: Fox5
So they're speeding up 2D graphics and cutting down on system memory usage...
Well nice upgrades I suppose, but not enough to get me to buy another new OS. Ram is cheaper than Windows, and I can already have 50+ windows open with no lag.

You neglected the GDI concurrency which is really a big deal.
Vista has a very annoying practice where one application can take control of the display and not release it when you switch to another application. This often shows up as a white screen on the application that has the control. You can alt+tab and switch applications and sometimes that will fix it.

So they did this

GDI applications running simultaneously vie for this global lock in order to render on the screen. The application that accesses the global lock prevents other applications from rendering till it releases the global lock.

Without the Windows 7 GDI concurrency, the rendering throughput of these applications is effectively limited to the performance of a single CPU core. Since only a single application can acquire the global exclusive lock while the others are waiting, this scenario doesn?t benefit from multiple CPU cores. This demonstrates that GDI applications in Windows 7 are now much less dependent on one another. This benefit will not need any new display drivers; it will work on any Vista (WDDM 1.0) and newer display drivers.

GDI is not a API now that is separate from Aero, it is tightly integrated.


The changes speed up every window on the desktop . You could have 10GB of ram and the way 7 implements the subsystem would still be faster. Rendering windows with hardware will always be faster than software.

GDI is being rendered utilizing the CPU completely in the operating system without any assistance or ?acceleration? by the graphics hardware. As the CPU performs all the tasks for rendering GDI applications, it requires an easily accessible cacheable copy of memory.

Based on real-world application statistics, a tiny snapshot of which is seen above, we worked with our graphics IHV partners to provide support in their drivers to accelerate the most commonly used GDI operations. Windows 7 systems with these updated drivers, called ?WDDM v1.1? will thus benefit from this memory savings work.

Everyone interested should take a look at the powerpoint from winhec.
http://www.google.com/url?sa=t...UCsdCJV8tGUtQPy9VLCAHA