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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  • nitrousoxide - Tuesday, November 09, 2010 - link

    Delaying is something good because it indicates that Cayman can be very big, very fast and...very hungry making it hard to build. What AMD needs is a card that can defeat GTX580, no matter how hot or power-hungry it is. Reply
  • GeorgeH - Tuesday, November 09, 2010 - link

    Is there any word on a fully functional GF104?

    Nvidia could call it the 560, with 5="Not Gimped".
    Reply
  • Sihastru - Tuesday, November 09, 2010 - link

    I guess once GTX470 goes EOL. If GTX460 had all it's shaders enabled then the overclocked versions would have canibalized GTX470 sales. Even so, it will happen on occasion. Reply
  • tomoyo - Tuesday, November 09, 2010 - link

    My guess is there will be GTX 580 derivatives with less cores enabled as usual, probably a GTX 570 or something. And then an improved GTX 460 with all cores enabled as the GTX 560. Reply
  • tomoyo - Tuesday, November 09, 2010 - link

    Good to see nvidia made a noticeable improvement over the overly hot and power hungry GTX 480. Unfortunately way above my power and silence needs, but competition is a good thing. Now I'm highly curious how close the Radeon 69xx will come in performance or if it can actually beat the GTX 580 in some cases.
    Of course the GTX 480 is completely obsolete now, more power, less speed, more noise, ugly to look at.
    Reply
  • 7eki - Tuesday, November 09, 2010 - link

    What we got here today is a higher clocked, better cooled GTX 480 with a slightly better power consumption. All of that for only 80$ MORE ! Any first served version of non referent GTX 480 is equipped with a much better cooling solution that gives higher OC possibilites and could kick GTX 580's ass. If we compare GTX 480 to a GTX580 clock2clock we will get about 3% of a difference in performance. All thanks to 32 CUDA processors, and a few more TMU's. How come the reviewers are NOW able to find pros of something that they used to criticise 7 months ago ? Don't forget that AMD's about to break their Sweet Spot strategy just to cut your hypocrites tongues. I bet that 6990's going to be twice as fast as what we got here today . If we really got anything cause I can't really tell the difference. Reply
  • AnnonymousCoward - Tuesday, November 09, 2010 - link

    32W less for 15% more performance, still on 40nm, is a big deal. Reply
  • 7eki - Wednesday, November 10, 2010 - link

    32W and 15% you say ? No it isn't a big deal since AMD's Barts GPUs release. Have on mind that GTX580 still consumes more energy than a faster (in most cases) and one year older multi GPU HD5970. In that case even 60 would sound ridiculosly funny. It's not more than a few percent improvement over GTX480. If you don't believe it calculate how much longer will you have to play on your GTX580 just to get your ~$40 spent on power consumption compared to a GTX480 back. Not to mention (again) that a nonreferent GTX480 provides much better cooling solutions and OC possibilities. Nvidia's diggin their own grave. Just like they did by releasing GTX460. The only thing that's left for them right now is to trick the reviewers. But who cares. GTX 580 isn't going to make them sell more mainstream GPUs. It isn't nvidia whos cutting HD5970 prices right now. It was AMD by releasing HD6870/50 and announcing 6970. It should have been mentioned by all of you reviewers who treat the case seriously. Nvidia's a treacherous snake and the reviewers job is not to let such things happen. Reply
  • Sihastru - Wednesday, November 10, 2010 - link

    Have you heard about the ASUS GTX580 Voltage Tweak edition that can be clocked up to 1100 MHz, that's more then 40% OC? Have you seen the EVGA GTX580 FTW yet?

    The fact that a single GPU card is in some cases faster then a dual GPU card built with two of the fastest competing GPU's tells a lot of good things about that single GPU card.

    This "nVidia in the Antichrist" speech is getting old. Repeating it all over the interwebs doesn't make it true.
    Reply
  • AnnonymousCoward - Wednesday, November 10, 2010 - link

    I'm with you, that AMD still has a superior performance per power design. But with the 580, nvidia took Fermi from being outrageous to competitive in that category, and even wins by a wide margin with idle power. Looking at the charts, the 580 also has a vastly superior cooling system to the 5970. Mad props to nvidia for turning things around. Reply

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