Mobile GPU Faceoff: AMD Dynamic Switchable Graphics vs. NVIDIA Optimus Technolog

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By Jarred Walton Switchable Graphics - Meet the Contenders 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 “fowl!”, let me explain. First, we asked AMD for just such a laptop back in May, and they haven’t been able to get use one yet (though it’s likely as much the fault of OEMs as AMD). We also only just received our first Sony laptop (from Sony) in a long while, and we received the VAIO C from NVIDIA first. Finally, the laptops came boxed up, unopened, with all the standard fluff you’d expect from retail notebooks. After unboxing, we did our usual thing: create a new user account, and then commence uninstalling the bloatware—and yes, the Sony VAIO C and Acer TimelineX 3830TG both have a lot of it!—and when all that is done and we’ve shut off any unnecessary applications and utilities, we start installing our benchmark suite. After that’s done, we do a full defrag (using Defraggler) and then we can start testing. Despite the source of the laptops, then, we are confident that both are reasonable representations of what you’ll get—actually, the TimelineX 3830TG has some issues with throttling in games, so if anything NVIDIA’s choice for their own platform wasn’t the best, though the Sony VAIO C may not be the greatest AMD offering either. In terms of other alternatives, while there are dozens of currently shipping Optimus laptops (ASUS, Clevo, Dell, HP, MSI, Samsung, Sony, Toshiba, and others are all onboard with the platform), finding laptops with Intel CPUs and AMD dynamic switchable graphics is a lot more difficult. Sony has the VAIO C—the VAIO S we recently reviewed doesn’t support dynamic switching, instead using the older manual switching—Dell has the Vostro 3550, and HP has it with certain dv6/dv7 series laptops. (Note: I’ve looked around for more details on which laptops support AMD’s Dynamic Switchable Graphics and came up empty, but if anyone can find a comprehensive list I’ll be happy to post it.) There may be a few other laptops out there with Intel CPUs and AMD 6000M GPUs—or rather, 6400M or 6600M GPUs; the 6300M and 6700M are actually rebadged 5400M/5600M GPUs and don’t support dynamic switching AFAICT—but there definitely aren’t as many options. We’ll be running a few benchmarks later, so while we’re on the subject of laptops, let’s go over the full specs. Starting with the AMD Sony VAIO CA laptop, here’s what we have: The OEM-only i5-2410M is a good entry-level Sandy Bridge processor, and pricing is only slightly higher than the base model i3-2310M (which is clocked at 2.1GHz and lacks Turbo Boost support). 4GB RAM is fine, and the HD 6630M is actually a fairly potent mobile GPU as we’ll see in a moment. The big problems with the VAIO CA are that it comes with a slow and rather outdated 320GB 5400RPM hard drive (Western Digital Blue) and it also has a ton of bloatware. The bloatware can be uninstalled, and we did that as our first priority, but the hard drive tended to be an ongoing concern. AMD’s Catalyst Control Center for instance pops up in a couple seconds on my desktop (Bloomfield + SSD + HD 6950), but on the VAIO C there are times when it can take upwards of 30 seconds (with the HDD activity light a solid orange). Games also tended to take a bit longer to load than we’re used to. Outside of those two areas, the VAIO C is pretty much standard consumer laptop fare: glossy 1366x768 LCD, decent but not exceptional build quality, and average speakers. The keyboard is decent, though I’d still prefer dedicated document navigation keys (rather than the Fn+cursor combinations Sony uses), and it does have nice backlighting. On the other side of the table is Acer’s TimelineX 3830TG-6431, priced over $200 cheaper than the Sony. Acer has a habit of releasing laptops and then discontinuing them not long after, only to replace them with slightly different models, so we can’t guarantee the 3830TG-6431 will always be in stock; however, it appears readily available right now. The AS3830TG-6431 has on serious problem, unfortunately: the CPU tends to throttle down to 1.2GHz when gaming as the CPU and GPU end up creating more heat than the system cooling can handle. That’s a real shame, as if it weren’t for the throttling there would be a lot to like with the 3830TG. For one, the floating island keyboard I detest so much on other Acer/Gateway laptops is gone, replaced by a chiclet-style keyboard. There’s a bit of flex but I can live with it, and the layout is good (except for the crazy backslash-joined-to-the-enter-key weirdness). This is also a very thin and light laptop, helped by the absence of an optical drive, and the dimensions would be very impressive given the i5-2410M CPU and GT 540M GPU if it weren’t for the thermal throttling problem. Acer gives the TimelineX an aluminum cover and palm rest as well, but the LCD is one of the worst I’ve used (poor viewing angles and weak colors, plus our sample has a red pixel in the middle center of the LCD that’s stuck). Because of the throttling issue, the 3830TG benchmarks aren’t the best representative of what you can get from NVIDIA’s GT 540M. We’ll include two other laptops with the GT 540M (and Optimus) in most of our benchmarks as alternative reference points: the Alienware M11x R3 (i7-2617M CPU) and the Dell XPS 15 L502x (i7-2630QM). In theory, the i5-2410M should sit somewhere in between these two in terms of performance, but the throttling drops it lower in most tests. However, if you’re willing to play around with a utility like ThrottleStop, you can actually get the CPU to run at a constant 2.1GHz without any throttling (basically using the i5-2410M as an i3-2310M CPU). We tested with ThrottleStop set at 2.1GHz along with running “stock” (e.g. with throttling) to provide a couple more points of reference in our gaming results. How 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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Closing Thoughts

This has been the first laptop with AMD switchable graphics that I’ve had a chance to actually review, and it hasn’t impressed me as much as I would like. I can’t say I’m really surprised, as I’ve been trying to get my hands on such a laptop since the HP Envy 14 launched. If it worked perfectly and could match NVIDIA’s Optimus, I imagine AMD and/or their partners would have been pushing it into reviewers’ hands a lot more. Regardless of delays in getting a test sample, we’ve finally had a chance to test AMD’s Dynamic Switchable Graphics and we can tell you where it stands…sort of. Let’s recap.

AMD’s dynamic switching is fine when it works, but in our testing it fails to work on a regular basis. Mostly, it just feels like it needs more development and testing; given sufficient resources and time all of the issues I’ve experienced on the VAIO C could get resolved. Long-term, AMD needs a lot more games to get explicit support; out of sixteen titles, not even counting OpenGL games, four of the games had some sort of problem with dynamic switching. On an NVIDIA Optimus laptop, every single game worked without any tweaking necessary. That’s what AMD needs to achieve at this point, and preferably do so without any performance compromises.

The bigger issue of course is that AMD needs to get their laptop partners—Sony in this case—to release regular driver updates, and to use up-to-date driver builds when laptops launch. For all we know many of the issues have been addressed in the months since the February build; instead, Sony has a driver released in June 2011, but with a version number that suggests it was already over four months old at the time the VAIO VPCCA290X launched. We found that the Llano A8-3500M with the HD 6630M outperformed the VAIO CA, which simply shouldn’t happen (unless AMD has some special optimization on Llano that allow their GPUs to run faster). It looks like Sony has given up at least 10% of the performance potential of HD 6630M on average, and in some games the outdated drivers may be culling a third of the performance potential.

That’s really my main concern if you haven’t noticed: drivers. If you have an AMD IGP and AMD GPU (e.g. Llano), some of this discussion becomes unnecessary. Since AMD provides both graphics drivers in that case, updates should be a lot easier, although OEMs would still need to sanction the reference drivers. If an OEM were willing to commit the resources necessary to at least do bi-monthly driver updates for switchable graphics, that would also be sufficient, but they’d need a proven track record of doing so—something no laptop manufacturer has ever achieved. Another alternative is for AMD to get the OEMs on board with letting AMD release reference drivers, including for switchable graphics platforms on Intel chipsets, but no one has managed to do that either and I don’t see things changing. As noted earlier, AMD already has plans in place to move to fully independent graphics drivers, hopefully some time in 2012, but best-case we’re four months away and worst-case it might not even happen in 2012.

That’s another part of the problem with AMD’s drivers, unfortunately: they currently have people working on Brazos, Llano, the upcoming Trinity, existing desktop and notebook graphics, the HD 7000 series, and switchable graphics (plus some other tidbits I missed I’m sure). I doubt that fixing their Dynamic Switchable Graphics drivers will take priority over getting HD 7000 and Trinity drivers ready, and AMD could probably use more people working on improved compiler support for Bulldozer while we’re at it. In other words, there are a lot of areas in AMD software development that need people, and how many people are working on Dynamic Switchable Graphics is unknown. NVIDIA’s Optimus Technology currently enjoys a healthy lead in dynamic switchable graphics and AMD is trying to play catch up, and I’m not sure they’re ready to commit the manpower required to make it happen. It’s hardly a surprise then that where more than 100 Optimus enabled laptops have launched in the past 18 months, there are only a few laptops with AMD’s Dynamic Switchable Graphics—and only a dozen or so laptops using any form of AMD switchable graphics to my knowledge.

As far as the VAIO CA goes, Sony makes a decent laptop—we’ll give it a separate review shortly. The VAIO CA isn’t at quite the same level in terms of build quality and materials as the VAIO SB Dustin reviewed, but it does provide reasonable performance and some of the best battery life results we’ve seen for the specs. If nothing else, Sony at least knows how to tune their laptops for long battery life. Pricing is where things get dicey; there are some $800 VAIO C models that have the same specs as the review unit, but it’s not clear if they include the HD 6630M or not—we’re guessing not. Going straight to Sony, you can configure the VPCCA290X with all the options of our review unit at a not-too-onerous price of $930. Where Sony completely fails however is in their driver support; shipping a laptop with discrete graphics using drivers that are at least four months old (at the time of launch) is tantamount to telling your customers that they don’t need the graphics card at all! But we say the same thing about HD 6470M and yet several companies (including Sony) are still using it.

Ironically, I’d rather have something like the HP Envy 14 or the Sony VAIO C without AMD’s switchable graphics and just give me a discrete GPU instead; that would make getting updated video drivers easier and battery life doesn’t even suffer all that much. AMD is actually a bit closer to my ideal of not needing switchable graphics than NVIDIA, as their mainstream GPUs tend to use less power. Their HD 6630M still draws about 2.0~2.3W more than Intel’s HD 3000 IGP under low loads and 2.8W more during H.264 decoding, but that compares to around 4.3W more for a GT 540M doing H.264 decoding. (We can’t test idle power draw since Optimus just shuts the dGPU off—not that that’s a bad thing.) Of course, the 6630M at ~8.3W idle is still using about 30% more total power than with the IGP (6.0W), but you can still get over six hours of battery life.

Given the price of $930 for the Sony VAIO C, at that point you’re within $150 of better built laptops with nice 1080p displays—e.g. the Dell XPS 15z, or wait for the XPS 14z to show up and see what it offers. If you don’t mind the CPU throttling (or at least running games while using ThrottleStop), you can also grab the Acer TimelineX 3830TG-6431 we used as a comparison point in this article for just $700. The MSI X460DX-008US for $727 (with i3-2310M and a 14” LCD), 15.6” Acer Aspire AS5750G-6496 for $680, or the 15.6” Gigabyte Q2532N-CF1 for $885 are also available for less money than the Sony—and that’s just naming a few of the Optimus laptops with Sandy Bridge CPUs and GeForce GT 540M GPUs. In short, you can get any laptop equipped with NVIDIA’s Optimus Technology and get the improved battery life that running off the IGP affords while still having readily available driver updates, frequently at a lower price. Unless you absolutely don’t care about driver updates—or a UI with lack of “expert” features like a list of game and application profiles and global settings—NVIDIA is definitely the way to go for dynamic switchable graphics technologies right now.

原文：
http://www.anandtech.com/show/4839/mobile-gpu-faceoff-amd-dynamic-switchable-graphics-vs-nvidia-optimus-technology/1