Virtual Memory

Microsoft is taking tighter control of graphics memory with it's new driver model, and thus is able to provide virtual memory support for the graphics memory subsystem. What this means is that games no longer need to worry about running out of graphics memory. When software needs to write something to local memory, and local memory is full, Windows will be able to kick out something off the graphics card and put it in system memory (this is called paging) until it is needed. This happens without the software's intervention or knowledge. If system memory becomes full, data will be kicked out to the hard drive. Of course, if something like this happens the performance will definitely suffer.

Virtual memory isn't as much a performance enhancing tool as it is a way to remove the burden on the developer to manage memory usage around a hard limit of available space. Certainly, lots of paging will degrade performance, but lower performance is generally better than a crash. On the flip side, it is possible that virtual memory could increase performance by effectively replacing local graphics memory size with unused PCIe bandwidth. This has been the idea behind TurboCache and HyperMemory, but with the added advantage that the graphics driver doesn't need to worry about object or texture management between local and system memory.

Engineers have been wanting to see virtualized graphics memory for years, as operating on really huge data sets is made significantly easier when the software developer doesn't have to manage moving data in and out of graphics memory by hand. We've seen some limited benefits of utilizing both local and system memory on low memory TurboCache and HyperMemory cards. With game developers reaching towards ever larger data sets, high end parts will soon begin to benefit from virtualized graphics memory as well. Building the hardware to accommodate the possibility of higher latencies due to paging and allowing the OS to manage all the memory in the system will definitely help developers focus on building better games rather than better memory managers. That's not to say that memory management won't still be important to game developers. Making sure space and bandwidth are used efficiently are important factors in performance, but the ability to forget about hard limits in local memory will make it easier to take one efficient approach regardless of onboard memory.

Hardware Virtualization

Lately, all the big boys of computing have been infatuated with the idea of virtualization. It makes a whole lot of sense, really. With the advent of multi-core CPUs, AMD and Intel need to find ways to take full advantage of their processing power. Single thread execution time will never disappear as a factor in computing, and some algorithms just can't be parallelized.

Obviously, encouraging users to multitask is a simple way to provide a benefit to multi-core computing. The next step is to encourage developers to write highly multithreaded applications. Beyond that is to allow the user to run multiple operating systems on one set of hardware. One example of how this may be beneficial is in the use of a single system as a normal PC during its use as a home theater / DVR box. Another example is one we've already seen: Mac users running both Windows and OS X on Intel based Macs using a virtual machine manager like Parallels.

In order to really achieve the capabilities hardware providers would like to promote, more work must be done by hardware, software, and operating system providers. One of the major advances necessary is the virtualization of the graphics subsystem. With DirectX10 and the new WDDM (Windows Display Driver Model), graphics hardware is required to support virtualization. This is not a simple request, as games will no longer be guaranteed exclusive access to the hardware while running. We can potentially share game rendering with something like physics calculations on the same GPU. Or we could run a Folding@Home GPU client in the background while we play a game. On the extreme, multiple full screen 3d applications could be running concurrently.

Drivers and hardware will have to support context switching on a massive scale due the huge number of pipelines and registers supported in DX10 class hardware. With the advent of features like TurboCache and HyperMemory (and now graphics memory virtualization), hardware developers are already prepared to handle much larger latencies than we've seen in the past. The ability to preempt a process on the GPU will only increase the potential latency that will need to be addressed.

This is another major step in bringing the GPU closer in functionality to the CPU. More attention must be paid not only to instruction and thread scheduling, but the scheduling of multiple programs. This is no small task when such a high number of pipelines need to be managed. We are very interested in discovering how well NVIDIA has implemented this feature, but we won't be able to test this until we have access to an operating system, API, and software that support it as well.

Index All GPUs are Created Equal: Say Goodbye to Cap Bits
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  • DerekWilson - Thursday, November 09, 2006 - link

    i'm sure there was a lot burried in there ... sorry if it wasn't easy to find.

    8800 gtx and gtx are both no louder than 7900 gtx. 1950 xtx still takes the cake for loudest graphics card around by a long shot -- especially after it heats up in a game.
    Reply
  • crystal clear - Thursday, November 09, 2006 - link

    My comments in Daily Tech on this subject-

    More "G80" Derivatives in February R
    E: More info would be nice
    By crystal clear on 11/8/06, Rating: 2
    By crystal clear on 11/8/2006 8:03:43 AM , Rating: 2

    If you link VISTA -SANTA ROSA platform-Core2DUO(merom)CPU line up(T7300,7500,7700 models)then a matching Graphics card
    to complete the link.

    So a G80 for laptops/notebooks?

    The pairing of Intels Santa Rosa platform with Vista in the 2Q 07 is next big thing for the first tier notebook manufacturers & all they need is a matching G80 for this setup.

    Unquote-
    Nvidia currently caters to Desktop requirement/needs with the new G80 releases,wonder how the notebook/server versions will be-with Vista ofcourse.



    Reply
  • yyrkoon - Thursday, November 09, 2006 - link

    Vitual memory is probably a good thing for most cases, but in the graphics arena, this *could* potentially make for sloppy/ bad coding practises. Knowing a lot of game devers (some of which actually work for well known companies), I've heard them from time to time complain about maxing a 16x PCI-E pipe. What I'm trying to say here, is that while it would be a good thing for never having to run out of texture memory, but that system memory, and definately the swap disk can not hold a candle to the memory bandwidth that most Video cards are capable of. End result, is that you definately *will* get a performance hit. All this, and we already know the memory bandwidth capabilities of modern PCs, suffice it to say, the most we'll see from current systems is what ? 12-13K GB/s ? Even a 7800GS can do roughly 35 GB/s on card. A 7600GT ? 22GB/s ?

    Still I think Directx10 is a very good thing, and as I didnt read the whole article, perhaps a missed a little ? Reason being, I've been reading about Directx10 since April, and a friend of mine was privy to some of this information after an interview with ATI.

    http://www.gamedev.net/reference/programming/featu...">http://www.gamedev.net/reference/programming/featu...
    Reply
  • saratoga - Thursday, November 09, 2006 - link

    I don't know how they threading really works, but its quite possible VM support is required in order to allow multiple threads to run without stepping all over each other,. Reply
  • saratoga - Thursday, November 09, 2006 - link

    Sorry, should read "I don't know how THEIR threading works" Reply
  • falc0ne - Thursday, November 09, 2006 - link

    I don't know what is the problem but I'm really unable to see the images within the latest articles from Anand...Can anyone give me a suggestion? What might be the cause of that?
    The thing is I'm really, really interested in these articles and I need to see those images. Thanks
    Reply
  • yyrkoon - Thursday, November 09, 2006 - link

    Oh, er, then in the options tab of Firefox, (tools->options->content) check the "load images" check box ;) Reply
  • falc0ne - Thursday, November 09, 2006 - link

    well...it would've been simple but I'm afraid is not that...It might be the addblock extension from firefox, other than that I have nooo ideeea...Well I will use the IE tab option instead and load the pages using IE 7. Thanks anyway:) Reply
  • yyrkoon - Thursday, November 09, 2006 - link

    Checked the exceptions list ? I know that firefox makes it really simple to block images from a site (to a point of being too easy). Reply
  • JarredWalton - Thursday, November 09, 2006 - link

    If you've got AdBlock on Firefox, press Ctrl+Shift+A and you can see what it's blocking. If it blocks the images.anandtech.com stuff, you can then see which RegEx isn't working right and edit that. Reply

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