NVIDIA's Fermi: Architected for Tesla, 3 Billion Transistors in 2010
by Anand Lal Shimpi on September 30, 2009 12:00 AM EST- Posted in
- GPUs
Architecting Fermi: More Than 2x GT200
NVIDIA keeps referring to Fermi as a brand new architecture, while calling GT200 (and RV870) bigger versions of their predecessors with a few added features. Marginalizing the efforts required to build any multi-billion transistor chip is just silly, to an extent all of these GPUs have been significantly redesigned.
At a high level, Fermi doesn't look much different than a bigger GT200. NVIDIA is committed to its scalar architecture for the foreseeable future. In fact, its one op per clock per core philosophy comes from a basic desire to execute single threaded programs as quickly as possible. Remember, these are compute and graphics chips. NVIDIA sees no benefit in building a 16-wide or 5-wide core as the basis of its architectures, although we may see a bit more flexibility at the core level in the future.
Despite the similarities, large parts of the architecture have evolved. The redesign happened at low as the core level. NVIDIA used to call these SPs (Streaming Processors), now they call them CUDA Cores, I’m going to call them cores.
All of the processing done at the core level is now to IEEE spec. That’s IEEE-754 2008 for floating point math (same as RV870/5870) and full 32-bit for integers. In the past 32-bit integer multiplies had to be emulated, the hardware could only do 24-bit integer muls. That silliness is now gone. Fused Multiply Add is also included. The goal was to avoid doing any cheesy tricks to implement math. Everything should be industry standards compliant and give you the results that you’d expect.
Double precision floating point (FP64) performance is improved tremendously. Peak 64-bit FP execution rate is now 1/2 of 32-bit FP, it used to be 1/8 (AMD's is 1/5). Wow.
NVIDIA isn’t disclosing clock speeds yet, so we don’t know exactly what that rate is yet.
In G80 and GT200 NVIDIA grouped eight cores into what it called an SM. With Fermi, you get 32 cores per SM.
The high end single-GPU Fermi configuration will have 16 SMs. That’s fewer SMs than GT200, but more cores. 512 to be exact. Fermi has more than twice the core count of the GeForce GTX 285.
| Fermi | GT200 | G80 | |
| Cores | 512 | 240 | 128 |
| Memory Interface | 384-bit GDDR5 | 512-bit GDDR3 | 384-bit GDDR3 |
In addition to the cores, each SM has a Special Function Unit (SFU) used for transcendental math and interpolation. In GT200 this SFU had two pipelines, in Fermi it has four. While NVIDIA increased general math horsepower by 4x per SM, SFU resources only doubled.
The infamous missing MUL has been pulled out of the SFU, we shouldn’t have to quote peak single and dual-issue arithmetic rates any longer for NVIDIA GPUs.
NVIDIA organizes these SMs into TPCs, but the exact hierarchy isn’t being disclosed today. With the launch's Tesla focus we also don't know specific on ROPs, texture filtering or anything else related to 3D graphics. Boo.
A Real Cache Hierarchy
Each SM in GT200 had 16KB of shared memory that could be used by all of the cores. This wasn’t a cache, but rather software managed memory. The application would have to knowingly move data in and out of it. The benefit here is predictability, you always know if something is in shared memory because you put it there. The downside is it doesn’t work so well if the application isn’t very predictable.
Branch heavy applications and many of the general purpose compute applications that NVIDIA is going after need a real cache. So with Fermi at 40nm, NVIDIA gave them a real cache.
Attached to each SM is 64KB of configurable memory. It can be partitioned as 16KB/48KB or 48KB/16KB; one partition is shared memory, the other partition is an L1 cache. The 16KB minimum partition means that applications written for GT200 that require 16KB of shared memory will still work just fine on Fermi. If your app prefers shared memory, it gets 3x the space in Fermi. If your application could really benefit from a cache, Fermi now delivers that as well. GT200 did have an L1 texture cache (one per TPC), but the cache was mostly useless when the GPU ran in compute mode.
The entire chip shares a 768KB L2 cache. The result is a reduced penalty for doing an atomic memory op, Fermi is 5 - 20x faster here than GT200.
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AtwaterFS - Wednesday, September 30, 2009 - link
4 reals - this dude is clearly an Nvidia shill.Question is, do you really want to support a company that routinely supports this propaganda blitz on the comments of every Fn GPU article?
It just feels dirty doesn't it?
strikeback03 - Thursday, October 1, 2009 - link
I doubt SiliconDoc is actually paid by nvidia, I've met people like this in real life who just for some reason feel a need to support one company fanatically.Or he just enjoys ticking others off. One of my friends while playing Call of Duty sometimes just runs around trying to tick teammates off and get them to shoot back at him.
SiliconDoc - Thursday, October 1, 2009 - link
If facing the truth and the facts makes you mad, it's your problem, and your fault.I certainly know of people like you describe, and let's face it, it is one of YOUR TEAMMATES---
--
Now, when you collective liars and deniars counter one of my pointed examples, you can claim something. Until then, you've got nothing.
And those last 3 posts, yours included, have nothing, except in your case, it shows what you hang with, and that pretty much describes the lies told by the ati fans, and how they work.
I have no doubt pointing them out "ticks them off".
The simple fix is, stop lying.
Yangorang - Wednesday, September 30, 2009 - link
Honestly all I want to know is:When will it launch? (as in be available for actual purchase)
How much will it cost?
Will this beast even fit into my case...and how much power will it use?
How will it perform? (particularly I'm wondering about DX11 games...as it seems to be very much a big deal for ATI)
but heh none of these questions will be answered for a while I guess....
I'm also kinda wondering about:
How does the GT300 handle tessellation?
Does it feature Angle-Independent Anisotropic Filtering?
I could really couldn't give a crap less about using my GPU for general computing purposes....I just want to play some good looking games without breaking the bank...
haukionkannel - Thursday, October 1, 2009 - link
Well it's going to be DX11 card, so it can handle tessalation. How well? That remains to be seen, but there is enough computing power to do it guite nicely.But the big guestion is not, if the GT300 is faster than 5870 or not, It most propably is, but how much and how much it does cost...
If you can buy two 5870 for the prize of GT300, it has to be really fast!
Interesting release and good article to reveal the architecture behind this chip. I am sure, that we will see more new around the release of Win7, even if the card is not released until 2010. Just to make sure, that not too many "potential" customers does not buy ATI made card by that time.
Allso as someone said before this seams to be guite modular, so it's possible to see some cheaper cut down versions allso. We need competition to low and middle range allso. Can G300 design do it reamains to be seeing.
SiliconDoc - Thursday, October 1, 2009 - link
Well, that brings to mind another anandtech LIE.--
In the 5870 article text post area, the article writer and tester, responded to a query by one of the fans, and claimed the 5870 is "the standard 10.5 " .
Well, it is NOT. It is OVER 11", and it is longer than the 285, by a bit.
So, I just have to shake my head, and no one should have wonder why. Even lying about the length of the ati card. It is nothing short of amazing.
silverblue - Thursday, October 1, 2009 - link
http://vr-zone.com/articles/sapphire-ati-radeon-hd...They say 10.5".
SiliconDoc - Thursday, October 1, 2009 - link
I'm sorry, I realize I left with you in the air, since you're so convinced I don't know what I'm talking about." The card that we will be showing you today is the reference Radeon HD 5870, which is a dual-slot graphics card that measures in at 11.1" in length. "
http://www.legitreviews.com/article/1080/2/">http://www.legitreviews.com/article/1080/2/
I mean really, you should have given up a long time ago.
silverblue - Friday, October 2, 2009 - link
Anand, could you or Ryan come back to us with the exact length of the reference 5870, please? I know Ryan put 10.5" in the review but I'd like to be sure, please.It's best to check with someone who actually has a card to measure.
silverblue - Friday, October 2, 2009 - link
You know something? I'm just going to back down and say you're right. You might just be, but I couldn't give a damn anymore.