Keeping It Cool: Transistors, Throttles, and Coolers

Beyond the specific architectural improvements for GF110 we previously discussed, NVIDIA has also been tinkering with their designs at a lower level to see what they could do to improve their performance in conjunction with TSMC’s 40nm manufacturing process. GF100/GTX480 quickly gathered a reputation as a hot product, and this wasn’t an unearned reputation. Even with an SM fused off, GTX 480 already had a TDP of 250W, and the actual power draw could surpass that in extreme load situations such as FurMark.

NVIDIA can (and did) tackle things on the cooling side of things by better dissipating that heat, but keeping their GPUs from generating it in the first place was equally important. This was especially important if they wanted to push high-clocked fully-enabled designs on to the consumer GeForce and HPC Tesla markets, with the latter in particular not being a market where you can simply throw more cooling at the problem. As a result NVIDIA had to look at GF110 at a transistor level, and determine what they could do to cut power consumption.

Semiconductors are a near-perfect power-to-heat conversion device, so a lot of work goes in to getting as much work done with as little power as necessary. This is compounded by the fact that dynamic power (which does useful work) only represents some of the power used – the rest of the power is wasted as leakage power. In the case of a high-end GPU NVIDIA doesn’t necessarily want to reduce dynamic power usage and have it impact performance, instead they want to go after leakage power. This in turn is compounded by the fact that leaky transistors and high clocks are strange bedfellows, making it difficult to separate the two. The result is that leaky transistors are high-clocking transistors, and vice versa.


A typical CMOS transitor: Thin gate dielectrics lead to leakage

Thus the trick to making a good GPU is to use leaky transistors where you must, and use slower transistors elsewhere. This is exactly what NVIDIA did for GF100, where they primarily used 2 types of transistors differentiated in this manner. At a functional unit level we’re not sure which units used what, but it’s a good bet that most devices operating on the shader clock used the leakier transistors, while devices attached to the base clock could use the slower transistors. Of course GF100 ended up being power hungry – and by extension we assume leaky anyhow – so that design didn’t necessarily work out well for NVIDIA.

For GF110, NVIDIA included a 3rd type of transistor, which they describe as having “properties between the two previous ones”. Or in other words, NVIDIA began using a transistor that was leakier than a slow transistor, but not as leaky as the leakiest transistors in GF100. Again we don’t know which types of transistors were used where, but in using all 3 types NVIDIA ultimately was able to lower power consumption without needing to slow any parts of the chip down. In fact this is where virtually all of NVIDIA’s power savings come from, as NVIDIA only outright removed few if any transistors considering that GF110 retains all of GF100’s functionality.

Of course reducing leakage is one way to reduce power consumption, but it doesn’t solve NVIDIA’s other problems in hitting their desired TDP. Both NVIDIA and AMD base their GPU TDP specifications around “real world” applications and games, with NVIDIA largely viewed to be more aggressive on this front. In either case load-generating programs like FurMark and OCCT do not exist in AMD or NVIDIA’s worlds, leading both companies to greatly despise these programs and label them as “power viruses” and other terms.

After a particularly rocky relationship with FurMark blowing up VRMs on the Radeon 4000 series, AMD instituted safeties in their cards with the 5000 series to protect against FurMark – AMD monitored the temperature of the VRMs, and would immediately downclock the GPU if the VRM temperatures exceeded specifications. Ultimately as this was temperature based AMD’s cards were allowed to run to the best of their capabilities, so long as they weren’t going to damage themselves. In practice we rarely encountered AMD’s VRM protection even with FurMark except in overclocking scenarios, where overvolting cards such as the 5970 quickly drove up the temperature of the VRMs.

For GTX 580 NVIDIA is taking an even more stringent approach than AMD, as they’ll be going after power consumption itself rather than just focusing on protecting the card. Attached to GTX 580 are a series of power monitoring chips, which monitor the amount of power the card is drawing from the PCIe slot and PCIe power plugs. By collecting this information NVIDIA’s drivers can determine if the card is drawing too much power, and slow the card down to keep it within spec. This kind of power throttling is new for GPUs, though it’s been common with CPUs for a long time.

NVIDIA’s reasoning for this change doesn’t pull any punches: it’s to combat OCCT and FurMark. At an end-user level FurMark and OCCT really can be dangerous – even if they can’t break the card any longer, they can still cause other side-effects by drawing too much power from the PSU. As a result having this protection in place more or less makes it impossible to toast a video card or any other parts of a computer with these programs.  Meanwhile at a PR level, we believe that NVIDIA is tired of seeing hardware review sites publish numbers showcasing GeForce products drawing exorbitant amounts of power even though these numbers represent non-real-world scenarios. By throttling FurMark and OCCT like this, we shouldn’t be able to get their cards to pull so much power. We still believe that tools like FurMark and OCCT are excellent load-testing tools for finding a worst-case scenario and helping our readers plan system builds with those scenarios in mind, but at the end of the day we can’t argue that this isn’t a logical position for NVIDIA.


Power Monitoring Chips Identified

While this is a hardware measure the real trigger is in software. FurMark and OCCT are indeed throttled, but we’ve been able to throw other programs at the GTX 580 that cause a similar power draw. If NVIDIA was actually doing this all in hardware everything would be caught, but clearly it’s not. For the time being this simplifies everything – you need not worry about throttling in anything else whatsoever – but there will be ramifications if NVIDIA actually uses the hardware to its full potential.

Much like GDDR5 EDC complicated memory overclocking, power throttling would complicate overall video card overclocking, particularly since there’s currently no way to tell when throttling kicks in. On AMD cards the clock drop is immediate, but on NVIDIA’s cards the drivers continue to report the card operating at full voltage and clocks. We suspect NVIDIA is using a NOP or HLT-like instruction here to keep the card from doing real work, but the result is that it’s completely invisible even to enthusiasts. At the moment it’s only possible to tell if it’s kicking in if an application’s performance is too low. It goes without saying that we’d like to have some way to tell if throttling is kicking in if NVIDIA fully utilizes this hardware.

Finally, with average and maximum power consumption dealt with, NVIDIA turned to improving cooling on the GTX to bring temperatures down and to more quietly dissipate heat. GTX 480 not only was loud, but it had an unusual cooling design that while we’re fine with, ended up raising eyebrows elsewhere. Specifically NVIDIA had heatpipes sticking out of the GTX 480, an exposed metal grill over the heatsink, and holes in the PCB on the back side of the blower to allow it to breathe from both sides. Considering we were dissipating over 300W at times it was effective, but apparently not a design NVIDIA liked.

So for GTX 580 NVIDIA has done a lot of work under the hood to produce a card that looks less like the GTX 480 and more like the all-enclosed coolers we saw with the GTX 200 series; the grill, external heatpipes, and PCB ventilation holes are all gone from the GTX 580, and no one would hold it against you to mistake it for a GTX 285. The biggest change in making this possible is NVIDIA’s choice of heatsink: NVIDIA has ditched traditional heatpipes and gone to the new workhorse of vapor chamber cooling.


A Vapor Chamber Cooler In Action (Courtesy NVIDIA)

 


The GTX 580's Vapor Chamber + Heatsink

Vapor chamber coolers have been around for quite some time as aftermarket/custom coolers, and are often the signature design element for Sapphire; it was only more recently with the Radeon HD 5970 that we saw one become part of a reference GPU design. NVIDIA has gone down the same road and is now using a vapor chamber for the reference GTX 580 cooler. Visually this means the heatpipes are gone, while internally this should provide equal if not better heat conduction between the GPU’s heatspreader and the aluminum heatsink proper. The ultimate benefit from this being that with better heat transfer it’s not necessary to run the blower so hard to keep the heatsink cooler in order to maximize the temperature difference between the heatsink and GPU.

NVIDIA’s second change was to the blower itself, which is the source of all noise. NVIDIA found that the blower on the GTX 480 was vibrating against itself, producing additional noise and in particular the kind of high-pitch whining that makes a cooler come off as noisy. As a result NVIDIA has switched out the blower for a slightly different design that keeps a ring of plastic around the top, providing more stability. This isn’t a new design – it’s on all of our Radeon HD 5800 series cards – but much like the vapor chamber this is the first time we’ve seen it on an NVIDIA reference card.

Top: GTX 480 Blower. Bottom: GTX 580 Blower

Finally, NVIDIA has also tinkered with the shape of the shroud encasing the card for better airflow. NVIDIA already uses a slightly recessed shroud near the blower in order to allow some extra space between it and the next card, but they haven’t done anything with the overall shape until now. Starting with the GTX 580, the shroud is now slightly wedge-shaped between the blower and the back of the card; this according to NVIDIA improves airflow in SLI setups where there’s a case fan immediately behind the card by funneling more fresh air in to the gap between cards.

GF110: Fermi Learns Some New Tricks Meet the GTX 580
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  • cjb110 - Tuesday, November 09, 2010 - link

    "While the difference is’ earthshattering, it’s big enough..." nt got dropped, though not yet at my workplace:) Reply
  • Invader Mig - Tuesday, November 09, 2010 - link

    I don't know the stance on posting links to other reviews since I'm a new poster, so I wont. I would like to make note that in another review they claim to have found a work around the power throttling that allowed them to use furmark to get accurate temps and power readings. This review has the 580 at 28w above the 480 at max load. I don't mean to step on anyone's toe's, but I have seen so many different numbers because of this garbage nvidia has pulled, and the only person who claims to have furmark working gets higher numbers. I would really like to see something definitive. Reply
  • 7Enigma - Tuesday, November 09, 2010 - link

    Here's my conundrum. What is the point of something like Furmark that has no purpose except to overstress a product? In this case the 580 (with modified X program) doesn't explode and remains within some set thermal envelope that is safe to the card. I like using Crysis as it's a real-world application that stresses the GPU heavily.

    Until we have another game/program that is used routinely (be it game or coding) that surpasses the heat generation and power draw of Crysis I just don't see the need to try to max out the cards with a benchmark. OC your card to the ends of the earth and run something real, that is understandable. But just using a program that has no real use to artificially create a power draw just doesn't have any benefit IMO.
    Reply
  • Gonemad - Tuesday, November 09, 2010 - link

    I beg to differ. (be careful, high doses of flaming.)

    Let me put it like this. The Abrams M1 Tank is tested on a 60º ramp (yes, that is sixty degrees), where it must park. Just park there, hold the brakes, and then let go. It proves the brakes on a 120-ton 1200hp vehicle will work. It is also tested on emergency brakes, where this sucker can pull a full stop from 50mph on 3 rubber-burning meters. (The treads have rubber pads, for the ill informed).
    Will ever a tank need to hold on a 60º ramp? Probably not. Would it ever need to come to a screeching halt in 3 meters? In Iraqi, they probably did, in order to avoid IEDs. But you know, if there were no prior testing, nobody would know.

    I think there should be programs specifically designed to stress the GPU in unintended ways, and it must protect itself from destruction, regardless of what code is being thrown at it. NVIDIA should be grateful somebody pointed that out to them. AMD was thankful when they found out the 5800 series GPUs (and others, but this was worse) had lousy performance on 2D acceleration, or none at all, and rushed to fix its drivers. Instead, NVIDIA tries to cheat Furmark by recognizing its code and throttling. Pathetic.

    Perhaps someday, a scientific application may come up with repeatable math operations that just behave exactly like Furmark. So, out of the blue, you got a $500 worth of equipment that gets burned out, and nobody can tell why??? Would you like that happening to you? Wouldn't you like to be informed that this or that code, at least, could destroy your equipment?

    What if Furmark wasn't designed to stress GPUs, but it was an actual game, (with furry creatures, lol)?

    Ever heard of Final Fantasy XIII killing off PS3s for good, due to overload, thermal runaway, followed by meltdown? Rumors are there, if you believe them is entirely to you.

    Ever heard of Nissan GTR (skyline) being released with a top-speed limiter with GPS that unlocks itself when the car enters the premises of Nissan-approved racetracks? Inherent safety, or meddling? Can't you drive on a Autoban at 300km/h?

    Remember back in the day of early benchmark tools, (3DMark 2001 if I am not mistaken), where the Geforce drivers detected the 3DMark executable and cheated the hell out of the results, and some reviewers got NVIDIA red-handed when they renamed and changed the checksum of the benchmark??? Rumors, rumors...

    The point is, if there is a flaw, a risk of an unintended instruction kill the hardware, the buyer should be rightfully informed of such conditions, specially if the company has no intention at all to fix it. Since Anand warned us, they will probably release the GTX 585 with full hardware thermal safeties. Or new drivers. Or not.

    Just like the instruction #PROCHOT was inserted in the Pentium (which version?) and some reviewers tested it against an AMD chip. I never forgot that AMD processor billowing blue smoke the moment the heatsink was torn off. Good PR, bad PR. The video didn´t look fake to me back then, just unfair.

    In the end, it becomes matter of PR. If suddenly all the people that played Crysis on this card caused it to be torched, we would have something really interesting.
    Reply
  • Sihastru - Tuesday, November 09, 2010 - link

    AMD has a similar system in place since the HD4xx0 generation. Remember when Furmark used to blow up 48x0 cards? Of course not. But look it up...

    What nVidia did here is what AMD has in all their mid/high end cards since HD4xx0. At least nVidia will only throttle when it detects Furmark/OCCT. AMD cards will throttle in any situation if the power limiter requires it.
    Reply
  • JimmiG - Tuesday, November 09, 2010 - link

    It's a very unfortunate situation that both companies are to blame for. That's what happens when you push the limits of power consumption and heat output too far while at the same time trying to keep manufacturing costs down.

    The point of a stress test is to push the system to the very limit (but *not* beyond it, like AMD and Nvidia would have you believe). You can then be 100% assured that it will run all current and future games and HPC applications, not matter what unusual workloads they dump on your GPU or CPU, without crashes or reduced performance.
    Reply
  • cactusdog - Tuesday, November 09, 2010 - link

    So if you want to use multiple monitors do you still need 2 cards to run it or have they enabled a third monitor on the 580? Reply
  • Sihastru - Tuesday, November 09, 2010 - link

    Yes. Reply
  • Haydyn323 - Tuesday, November 09, 2010 - link

    The 580 as with the previous generation still only supports 2 monitors max per card. Reply
  • Pantsu - Tuesday, November 09, 2010 - link

    A good article, and a good conclusion overall. Much better that the fiasko that was the 6800-article.

    I do lament the benchmarking method AT uses though. Benchmarks like the Crysis Warhead one are not really representative of real world performance, but tend to be a bit too "optimized". They do not reflect real world performance very well, and even skew the results between cards.
    Reply

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