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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  • dtham - Tuesday, November 09, 2010 - link

    Anyone know if aftermarket cooling for the GTX 480 will work for the GTX 580? It would be great to be able to reuse a waterblock from a GTX 480 for the new 580s. Looking at the picture the layout looks similar. Reply
  • mac2j - Tuesday, November 09, 2010 - link

    In Europe the GTX 580 was launched at 399 Euros and in response ATI has lowered the 5970 to 389 Euros (if you believe the rumors).

    This can only bode well for holiday prices of the 6970 vs 580.
    Reply
  • samspqr - Tuesday, November 09, 2010 - link

    it's already listed and in stock at alternate.de, but the cheapest one is 480eur

    the only 5970 still in stock there is 540eur
    Reply
  • yzkbug - Tuesday, November 09, 2010 - link

    I moved all my gaming to the living room on a big screen TV and HTPC (a next next gen console in a sense). But, Optimus would be the only way to use this card on HTPC. Reply
  • slatr - Tuesday, November 09, 2010 - link

    Ryan,

    Would you be able to test with Octane Renderer?

    I am interested to see if Octane gets throttled.

    Thanks
    Reply
  • Andyburgos - Tuesday, November 09, 2010 - link

    Ryan:

    I hold you in the most absolute respect. Actually, in my first post a while ago I praised your work, and I think you´re quite didactic and fun to read. On that, thanks for the review.

    However, I need to ask you: W.T.F. is wrong with you? Aren´t you pissed off by the fact that GTX480 was a half baked chip (wouldn´t say the same about GTX460) and now that we get the real version they decided to call it 580? Why isn´t a single complain about that in the article?

    If, as I understand, you think that the new power / temperature / noise / performance balance has improved dramatically from the 480, I think you are smart enough to see that it was because the 480 was very, very, unpolished chip. This renaming takes us for stupid, is even worse than what AMD did.

    /rant

    AT & staff, I think you have a duty to tell off lousy tactics such as the Barts being renamed 68x0, or the 8800 becoming 9800 then GTS250 as you always did. You have failed so badly to do that here that you look really biased. For me, a loyal argentinian reader since 2001, that is absolutely imposible, but with the GXT460 and this you are acomplishing that.

    +1 for this card deserving an indifferent thumbs up, as Ryan graciously said, not for the card itself (wich is great) but for the nVidia tactics and the half baked 480 they gave us. Remember the FX5800 (as bad or worse than the 480) becoming the 5900... gosh, I think those days are over. Maybe that´s why I stick with my 7300 GT, haha.

    I respectfully disent with your opinion, but thanks for the great review.

    Best regards,
    Andy
    Reply
  • ViRGE - Tuesday, November 09, 2010 - link

    Huh, are we reading the same article? See page 4. Reply
  • chizow - Tuesday, November 09, 2010 - link

    I'd have to agree he probably didn't read the article thoroughly, beside explicitly saying this is the 2nd worst excuse for a new naming denomination, Ryan takes jabs at the 480 throughout by repeatedly hinting the 580 is what Fermi should've been to begin with.

    Sounds like just another short-sighted rant about renaming that conveniently forgets all the renaming ATI has done in the past. See how many times ATI renamed their R200 and R300 designs, even R600 and RV670 fall into the same exact vein as the G92 renaming he bemoans......
    Reply
  • Haydyn323 - Tuesday, November 09, 2010 - link

    Nvidia has done no different than ATI has as far as naming in their new cards. They simply jumped on the naming bandwagon for marketing and competetive purposes since ATI had already done so.... at least the 580 is actually faster than the 480. ATI releasing a 6870 that is far inferior to a 5870 is worse in my mind.

    It should indeed have been a 485, but since ATI calls their new card a 6870 when it really should be a 5860 or something, it only seems fair.
    Reply
  • spigzone - Tuesday, November 09, 2010 - link

    Any 'bandwagon' here belongs to Nvidia. Reply

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