NVIDIA's GeForce GTX 580: Fermi Refined
by Ryan Smith on November 9, 2010 9:00 AM ESTGF110: Fermi Learns Some New Tricks
We’ll start our in-depth look at the GTX 580 with a look at GF110, the new GPU at the heart of the card.
There have been rumors about GF110 for some time now, and while they ultimately weren’t very clear it was obvious NVIDIA would have to follow up GF100 with something else similar to it on 40nm to carry them through the rest of the processes’ lifecycle. So for some time now we’ve been speculating on what we might see with GF100’s follow-up part – an outright bigger chip was unlikely given GF100’s already large die size, but NVIDIA has a number of tricks they can use to optimize things.
Many of those tricks we’ve already seen in GF104, and had you asked us a month ago what we thought GF110 would be, we were expecting some kind of fusion of GF104 and GF100. Primarily our bet was on the 48 CUDA Core SM making its way over to a high-end part, bringing with it GF104’s higher theoretical performance and enhancements such as superscalar execution and additional special function and texture units for each SM. What we got wasn’t quite what we were imagining – GF110 is much more heavily rooted in GF100 than GF104, but that doesn’t mean NVIDIA hasn’t learned a trick or two.
Fundamentally GF110 is the same architecture as GF100, especially when it comes to compute. 512 CUDA Cores are divided up among 4 GPCs, and in turn each GPC contains 1 raster engine and 4 SMs. At the SM level each SM contains 32 CUDA cores, 16 load/store units, 4 special function units, 4 texture units, 2 warp schedulers with 1 dispatch unit each, 1 Polymorph unit (containing NVIDIA’s tessellator) and then the 48KB+16KB L1 cache, registers, and other glue that brought an SM together. At this level NVIDIA relies on TLP to keep a GF110 SM occupied with work. Attached to this are the ROPs and L2 cache, with 768KB of L2 cache serving as the guardian between the SMs and the 6 64bit memory controllers. Ultimately GF110’s compute performance per clock remains unchanged from GF100 – at least if we had a GF100 part with all of its SMs enabled.
On the graphics side however, NVIDIA has been hard at work. They did not port over GF104’s shader design, but they did port over GF104’s texture hardware. Previously with GF100, each unit could compute 1 texture address and fetch 4 32bit/INT8 texture samples per clock, 2 64bit/FP16 texture samples per clock, or 1 128bit/FP32 texture sample per clock. GF104’s texture units improved this to 4 samples/clock for 32bit and 64bit, and it’s these texture units that have been brought over for GF110. GF110 can now do 64bit/FP16 filtering at full speed versus half-speed on GF100, and this is the first of the two major steps NVIDIA took to increase GF110’s performance over GF100’s performance on a clock-for-clock basis.
NVIDIA Texture Filtering Speed (Per Texture Unit) | |||||
GF110 | GF104 | GF100 | |||
32bit (INT8) | 4 Texels/Clock | 4 Texels/Clock | 4 Texels/Clock | ||
64bit (FP16) | 4 Texels/Clock | 4 Texels/Clock | 2 Texels/Clock | ||
128bit (FP32) | 1 Texel/Clock | 1 Texel/Clock | 1 Texel/Clock |
Like most optimizations, the impact of this one is going to be felt more on newer games than older games. Games that make heavy use of 64bit/FP16 texturing stand to gain the most, while older games that rarely (if at all) used 64bit texturing will gain the least. Also note that while 64bit/FP16 texturing has been sped up, 64bit/FP16 rendering has not – the ROPs still need 2 cycles to digest 64bit/FP16 pixels, and 4 cycles to digest 128bit/FP32 pixels.
It’s also worth noting that this means that NVIDIA’s texture:compute ratio schism remains. Compared to GF100, GF104 doubled up on texture units while only increasing the shader count by 50%; the final result was that per SM 32 texels were processed to 96 instructions computed (seeing as how the shader clock is 2x the base clock), giving us 1:3 ratio. GF100 and GF110 on the other hand retain the 1:4 (16:64) ratio. Ultimately at equal clocks GF104 and GF110 widely differ in shading, but with 64 texture units total in both designs, both have equal texturing performance.
Moving on, GF110’s second trick is brand-new to GF110, and it goes hand-in-hand with NVIDIA’s focus on tessellation: improved Z-culling. As a quick refresher, Z-culling is a method of improving GPU performance by throwing out pixels that will never be seen early in the rendering process. By comparing the depth and transparency of a new pixel to existing pixels in the Z-buffer, it’s possible to determine whether that pixel will be seen or not; pixels that fall behind other opaque objects are discarded rather than rendered any further, saving on compute and memory resources. GPUs have had this feature for ages, and after a spurt of development early last decade under branded names such as HyperZ (AMD) and Lightspeed Memory Architecture (NVIDIA), Z-culling hasn’t been promoted in great detail since then.
Z-Culling In Action: Not Rendering What You Can't See
For GF110 this is changing somewhat as Z-culling is once again being brought back to the surface, although not with the zeal of past efforts. NVIDIA has improved the efficiency of the Z-cull units in their raster engine, allowing them to retire additional pixels that were not caught in the previous iteration of their Z-cull unit. Without getting too deep into details, internal rasterizing and Z-culling take place in groups of pixels called tiles; we don’t believe NVIDIA has reduced the size of their tiles (which Beyond3D estimates at 4x2); instead we believe NVIDIA has done something to better reject individual pixels within a tile. NVIDIA hasn’t come forth with too many details beyond the fact that their new Z-cull unit supports “finer resolution occluder tracking”, so this will have to remain a mystery for another day.
In any case, the importance of this improvement is that it’s particularly weighted towards small triangles, which are fairly rare in traditional rendering setups but can be extremely common with heavily tessellated images. Or in other words, improving their Z-cull unit primarily serves to improve their tessellation performance by allowing NVIDIA to better reject pixels on small triangles. This should offer some benefit even in games with fewer, larger triangles, but as framed by NVIDIA the benefit is likely less pronounced.
In the end these are probably the most aggressive changes NVIDIA could make in such a short period of time. Considering the GF110 project really only kicked off in earnest in February, NVIDIA only had around half a year to tinker with the design before it had to be taped out. As GPUs get larger and more complex, the amount of tweaking that can get done inside such a short window is going to continue to shrink – and this is a far cry from the days where we used to get major GPU refreshes inside of a year.
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AnandThenMan - Wednesday, November 10, 2010 - link
"Relevent models only please, that have the same performance as the GTX580."So we can only compare cards that have the same performance. Exciting graphs that will make.
RobMel85 - Tuesday, November 9, 2010 - link
I browsed through the 10 pages of comments and I don't think I saw anyone comment on the fact that the primary reason Nvidia corrected their heat problem was by blatantly copying ATi/Sapphire...not only did they plagiarize the goodies under the hood, but they look identical to AMD cards now! Our wonderful reviewer made the point, but no one else seemed to play on it.I say weak-sauce for Nvidia, considering the cheapest 580 on NewEgg is $557.86 shipped; the price exceeds what 480 was initially and the modded/OC'd editions aren't even out yet. It can't support more than 2 monitors by itself and is lacking in the audio department. Yes, it's faster than it's predecessor. Yes, they fixed the power/heat/noise issues, but when you can get similar, if not better, performance for $200 less from AMD with a 6850 CF setup...it seems like a no brainer.
Sure ATi re-branded the new cards as the HD6000 series, but at least they aren't charging top $ for them. Yes, they are slower than the HD5000 series, but you can buy 2 6850s for less than the price of the 480, 580, 5970(even 5870 for some manufacturers) and see similar or better performance AND end up with the extra goodies the new cards support.
I am looking forward to the release of the 69XX cards to see how well they will hold up against the 580. Are they going to be a worthy successor to the 5900, or will they continue the trend of being a significant threat in CrossFire at a reasonable price? Only time will tell...
The real question is, what will happen when the 28nm HD7000 cards hit the market?
tomoyo - Tuesday, November 9, 2010 - link
Actually the newegg prices are because they have a 10% coupon right now. I bet they'll go back to closer to normal after the coupon expires...assuming there's any stock.Sihastru - Wednesday, November 10, 2010 - link
Vapour chamber cooling technology was NOT invented by ATI/Sapphire. They are NOT the first to use it. Convergence Tech, the owner of the patent, even sued ATI/Sapphire/HP because of the infringement (basically means stolen technology).LOL.
RobMel85 - Sunday, November 14, 2010 - link
Where within my post did I say it was invented by ATi/Sapphire...nowhere. The point that I was trying to make was that Nvidia copied the design that ATi/Sapphire had been using to trounce the Nvidia cards. The only reason they corrected their problems was by making their cards nearly identical to AMD/ATi...And to tomoyo, when I made that post there was no 10% coupon on newegg. They obviously added it because everyone else was selling them cheaper.
Belard - Wednesday, November 10, 2010 - link
This is still a "400" series part as it's really technically more advanced than the 480.Does it have additional features? No.
Is it faster, yes.
But check out the advancement feature list.
The 6800s, badly named and should have been 6700s, are slightly slower than the 5800s, but costs a lot less and actually does some things differently from the 5000 series. And sooner or later, there will be a whole family of 6000s.
But here we are, about 6months later and theres a whole new "product line"?
dvijaydev46 - Wednesday, November 10, 2010 - link
Is there any problem with Mediaespresso? My 5770 is faster with mediashow than mediaespresso. Can you check with mediashow to see if your findings are right?Oxford Guy - Wednesday, November 10, 2010 - link
The 480 beats the 580, except at 2560x1600. The difference is most dramatic at 1680x1050.http://techgage.com/reviews/nvidia/geforce_gtx_580...
http://techgage.com/reviews/nvidia/geforce_gtx_580...
http://techgage.com/reviews/nvidia/geforce_gtx_580...
Why is that?
Sihastru - Wednesday, November 10, 2010 - link
Proof that GF110 is not just a GF100 with all the shaders enabled.Oxford Guy - Wednesday, November 10, 2010 - link
This seems to me to be related to the slight shrinkage of the die. What was cut out? Is it responsible for the lower minimum frame rates in Unigine?