Mobile GPU Faceoff: AMD Dynamic Switchable Graphics vs. NVIDIA Optimus Technology
by Jarred Walton on September 20, 2011 6:40 AM ESTHow AMD’s Dynamic Switchable Graphics Works
One of the things we discussed with AMD was the technical details of their dynamic switchable graphics. At a high level, things might appear similar to NVIDIA’s Optimus, but dig a little deeper and you start to find differences. To recap how switchable graphics works, let’s start at the top.
The original switchable graphics technologies used the IGP and dedicated GPU as discrete devices. Both were connected to the necessary display outputs, with some hardware muxes that could select the active device. This requires more cost in the motherboard, and switching results in a blanking of the display as one device is deactivated and the other comes online. In the earliest implementations, you had to reboot when switching, and the system would start with either the IGP or dGPU active. Later implementations moved to software controlled muxes and dynamic switching, which required Windows Vista to work properly (since the IGP driver would unload, the GPU driver would start, and then the display content would activate on the GPU).
NVIDIA’s Optimus changes things quite a bit, as there are no longer any muxes. The display ports are always linked to the IGP output, and NVIDIA’s drivers simply look for calls to applications that the dedicated GPU can help accelerate. When they detect such an application—and the user can add their own custom apps—the drivers wake up the GPU and send it the rendering commands. The GPU does all of the necessary work, and then the result is copied directly into the IGP framebuffer, omitting any flickering or other undesirable effects as the IGP is constantly connected to the display output. The GPU can wake up in a fraction of a second, and when it’s no longer needed it will power down completely. NVIDIA even demonstrated this by removing the dGPU from a test system while it was powered on. The only catch is that the drivers need to have some knowledge of the applications/games in order to know when to use the GPU.
The details of AMD’s Dynamic Switchable Graphics are similar in practice to Optimus, but with a few differences. First, AMD always has both the IGP and GPU driver loaded, with a proxy driver funneling commands to the appropriate GPU. Where NVIDIA is able to completely power off the GPU under Optimus, AMD has modified their GPUs so that the PCI-E bus is isolated from the rest of the chip. Now when the GPU isn’t needed, everything powers down except for that PCI-E connection, so Windows doesn’t try to load/unload the GPU driver. The PCI-E link state gets retained, and a small amount (around 50mW) is needed to keep the PCI-E state active, but as far as Windows knows the GPU is still ready and waiting for input. AMD also informed us that their new GPUs use link adapter mode instead of multi adapter mode, and that this plays a role in their dynamic switchable graphics, but we didn’t receive any additional details on this subject.
As far as getting content from the dGPU to the display, the IGP always maintains a connection to the display ports, and it appears AMD’s drivers copy data over the PCI-E bus to the IGP framebuffer, similar to Optimus. Where things get interesting is that there are no muxes in AMD’s dynamic switchable graphics implementations, but there is still an option to fall back to manual switching. For this mode, AMD is able to use the display output ports of the Intel IGP, so their GPU doesn’t need separate output ports (e.g. with muxes). With the VAIO C, both dynamic and manual switching are supported, and you can set the mode as appropriate. Here are some static shots of the relevant AMD Catalyst Control Center screens.
In terms of the drivers, right now you get a single large driver package that includes a proxy driver, an Intel IGP driver, and AMD’s GPU driver all rolled into one. Long-term, AMD says they have plans to make their GPU driver fully independent from Intel’s IGP driver. They say this will only require some packaging updates and that they should make this change some time in 2012, but for now they continue to offer a monolithic driver package. OEMs apparently get this driver on a monthly basis (or can at least request it), but it’s up to the OEMs to validate the driver for their platform and release it to the public.
In the case of non-switchable graphics, AMD has a monthly driver update that we refer to as “reference drivers” that is publicly available. At present, you download a utility that will check your laptop GPU ID to see if the laptop is officially supported by the reference driver. Right now certain OEMs like to maintain control of the drivers so the AMD utility will refuse to download the full driver suite. In such cases, users have to wait for the manufacturers to roll out updates (Sony, Toshiba, and Panasonic all fall into this category). In the past, we have been able to download the reference driver using a “sanctioned” laptop (e.g. something from Acer), and we were able to install the reference driver on a non-sanctioned laptop. However, this does not work with switchable graphics laptops; you need the monolithic driver package for such systems.
That takes care of the high-level overview of how AMD’s Dynamic Switchable Graphics works, as well as a few other related items. The details are a little light, but that at least gives us an introduction to AMD’s current switchable graphics solutions. With the hardware and software discussions out of the way, let’s turn to our gaming results first and see how the two solutions and GPUs compare in performance as well as compatibility.
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Death666Angel - Wednesday, September 21, 2011 - link
"but then why even have dynamic switching in the first place?"That is a good question. I myself would prefer a solution that lets me decide what to do. I wouldn't prefer dynamic switching, because I want to be in control of my hardware as much as possible. Reboot switching is of course a pain in the butt, but I see nothing wrong with a short cut manual switch for iGPU/dGPU switching. Would be preferable to me actually.
But otherwise, thanks for the article.
mars2k - Wednesday, September 21, 2011 - link
I purchased a Lenovo W520 on the first day of release. Got the Thinkpad and could never get the graphics to perform correctly. Integration with the Intel board was lousy. Lenovo's support team could do nothing. I returned the machine. I'm thinking buggy drivers were the problem.My particular problem revolved around using multiple monitors. Connecting disconnecting or configuring multi monitors would often require a reboot. Worse than worthless!
Wolfpup - Wednesday, September 21, 2011 - link
“With all my talk of switchable graphics, though, let’s make one thing clear: switchable graphics is not necessarily the Holy Grail of mobile GPUs. The true ideal in my opinion is mobile GPUs that can run fast when needed (i.e. playing games), while also being able to power off large portions of the chip and RAM and get down to IGP levels of power consumption.”THANK you for that! That's the first time I've heard that said since all this switchable graphics stuff started.
As far as I'm concerned, the GPU situation on notebooks is a disaster, and right when I thought we were finally moving in the first direction, this switchable stuff came out.
As it is now, a HUGE percent of notebooks can't use Nvidia or AMD's normal drivers. Sandy Bridge + AMD shouldn't even be on the market, and shouldn't be considered by anyone. As the article mentions-you can't use normal drivers for those, at least not today. (AMD + AMD should work sooner or later, although the A series CPUs aren't listed yet in the driver download box on AMD.com...my little c50 notebook is supported though, so hopefully the A stuff will be soon too.)
I just bought Asus' G74, which I've really liked-and one of the reasons I bought it was that it DOESN'T use switchable graphics, and it DOES use normal drivers from Nvidia. Some more expensive systems with even better GPUs can't use the normal drivers, which IMO just isn't acceptable in a $1000 purchase, let alone a $2000+ purchase.
At any rate, Nvidia's current GPUs underclock themselves to a very impressive 50mhz, several times slower even than my Geforce 9650GT from 3 years back. As mentioned, get power gating in there, and just get rid of Optimus and AMD's equivalent. Get rid of that complexity, driver/compatibility weirdness, etc.
Even once switchable graphics are gone, we're STILL not there yet...as the article mentions, most of Sony and Toshiba's notebooks can't be updated. Sager's stuff apparently can't, etc.
My Asus N80 from 3 years ago and my G74 both accept Nvidia.com driver updates just like a desktop system, no hacks, nothing weird, it just works. And that's how it should be!
Anato - Friday, September 23, 2011 - link
Shouldn't be too difficult to make GPU which can divide resources so that parts of the unit can be shut down. Even CPU's can do that and they are executing same code as compared to GPU which can be more liberal on architecture.JonnyDough - Friday, September 23, 2011 - link
"If nothing else, Sony at least knows how to tune their laptops for long battery life."Now if they can just make PS3 networking that isn't so hackable, batteries that don't explode, and Blu-Ray discs that don't cost 4X as much as an up-scalable DVD. At least they are smart enough to partner up with AMD.
pman6 - Friday, September 23, 2011 - link
AMD's solution definitely seems half assed. Their drivers are always crap....just like how they rolled out the mobile llano hybrid crossfire with crap performance.
seems like they can never get the drivers right.
I have a llano laptop with crossfire, and you would think they would be able to do split frame rendering to improve performance. but 99% of the time, crossfire game performance is worse than discrete alone.
AMD needs to get their crap together.
netkcid - Friday, September 23, 2011 - link
good job trying to switch and run dx11 apps on a dx10 igp... and then complain about it...durJarredWalton - Saturday, September 24, 2011 - link
All of the games should run on the Intel IGP; none of them are DX11 only. Double dur. The point is that they're not switching over to the IGP when the laptop is set to do so. But that's not really the major issue -- if you're running a game, you'll want it on the dGPU 99% of the time. The real issue is that the dynamic switching failed to work properly. When the competition can make it work properly, and when your non-dynamic generally can work properly, then your drivers are not finished and certainly not worthy of WHQL certification (which has apparently become a joke these days).medi01 - Sunday, September 25, 2011 - link
"Before we get to the actual meat of this review, we have a disclaimer to make: both laptops we’re comparing came to us via NVIDIA. Now, before anyone cries “foul!”, let me explain..."Let me explain: AMD not sending you whatever you want is not a good enough reason to do hidden ads for nVidia.
JarredWalton - Tuesday, September 27, 2011 - link
Thanks for speaking for AMD, but I talked to them over four times throughout the course of this review. I've had this hardware since July, if that helps you figure out how much I've been waiting for AMD to step up with something better. In effect, I told AMD when I first got the laptop, "Look guys, I've got a Sony VAIO C with Intel + AMD dynamic switchable graphics, and there are problems. There are also no recent drivers. This review won't be favorable toward your solution if you can't get me something better." If I had given them a week, or even two, sure, but two months is more than enough time to give me something better if such a thing exists.Sticking up for AMD's solution just because it's from AMD is not a reason enough to do so. The solution as it currently stands is broken. It can be fixed, but until it actually IS fixed, I cannot recommend buying it. Like I said, I'd rather have AMD discrete GPU without switchable graphics on a laptop, because then at least I can get driver updates. And if you don't need driver updates, you don't really need a discrete GPU in your laptop.