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
A More Efficient Architecture
GPUs, like CPUs, work on streams of instructions called threads. While high end CPUs work on as many as 8 complicated threads at a time, GPUs handle many more threads in parallel.
The table below shows just how many threads each generation of NVIDIA GPU can have in flight at the same time:
| Fermi | GT200 | G80 | |
| Max Threads in Flight | 24576 | 30720 | 12288 |
Fermi can't actually support as many threads in parallel as GT200. NVIDIA found that the majority of compute cases were bound by shared memory size, not thread count in GT200. Thus thread count went down, and shared memory size went up in Fermi.
NVIDIA groups 32 threads into a unit called a warp (taken from the looming term warp, referring to a group of parallel threads). In GT200 and G80, half of a warp was issued to an SM every clock cycle. In other words, it takes two clocks to issue a full 32 threads to a single SM.
In previous architectures, the SM dispatch logic was closely coupled to the execution hardware. If you sent threads to the SFU, the entire SM couldn't issue new instructions until those instructions were done executing. If the only execution units in use were in your SFUs, the vast majority of your SM in GT200/G80 went unused. That's terrible for efficiency.
Fermi fixes this. There are two independent dispatch units at the front end of each SM in Fermi. These units are completely decoupled from the rest of the SM. Each dispatch unit can select and issue half of a warp every clock cycle. The threads can be from different warps in order to optimize the chance of finding independent operations.
There's a full crossbar between the dispatch units and the execution hardware in the SM. Each unit can dispatch threads to any group of units within the SM (with some limitations).
The inflexibility of NVIDIA's threading architecture is that every thread in the warp must be executing the same instruction at the same time. If they are, then you get full utilization of your resources. If they aren't, then some units go idle.
A single SM can execute:
| Fermi | FP32 | FP64 | INT | SFU | LD/ST |
| Ops per clock | 32 | 16 | 32 | 4 | 16 |
If you're executing FP64 instructions the entire SM can only run at 16 ops per clock. You can't dual issue FP64 and SFU operations.
The good news is that the SFU doesn't tie up the entire SM anymore. One dispatch unit can send 16 threads to the array of cores, while another can send 16 threads to the SFU. After two clocks, the dispatchers are free to send another pair of half-warps out again. As I mentioned before, in GT200/G80 the entire SM was tied up for a full 8 cycles after an SFU issue.
The flexibility is nice, or rather, the inflexibility of GT200/G80 was horrible for efficiency and Fermi fixes that.
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SiliconDoc - Thursday, October 1, 2009 - link
Well that's quite a compliment, thank you.Since you pretend to be a Kingslayer, I have to warn you, you have failed.
I am King, as you said, and in this case, your dullard's, idiotic attempt at another red raging rooster "silence job", has utterly failed.
Now, did you see that awesome closeup of TESLA ? You think that's carbon fiber at the bracket end ? Sure looks like it.
I wonder why ati only has like "red" "red" "red" "red" and "red" cards, don't you ?
I mean I never really thought about it before, but it IS LAME. It's like another cheapo low rent cost savings QUACK from the dollar undenominated lesser queendom of corner cutting, ati.
--
Gee, thank you for the added inspiration, as you well have noticed, the awful realities never mentioned keep coming to light.
At least one of us is actually thinking about videocards.
Not like you'll ever change that trend, so the King's Declaration is: EPIC FAIL !
tamalero - Thursday, October 1, 2009 - link
hu.. my 3870 from visiontek had black pbc :|SiliconDoc - Thursday, October 1, 2009 - link
Well that's actually kinda cool, but was the rest of it covered in that sick ati red ? That card is a heat monster with it's tiny core, so we know it was COVERED in fannage and plastic, unless it was a supercheap single slot that just blasted it into the case.BTW, in order to comment you've exposed another notch in your red fannage purchase history.
tamalero - Friday, October 2, 2009 - link
wait.. WHAT? o_Oyou dont make any sense.
silverblue - Thursday, October 1, 2009 - link
There's an nVidia card sat on a desk at work. It's got a red PCB.SiliconDoc - Thursday, October 1, 2009 - link
Yes, once again you made my point for me, and being so ignorant you failed to notice ! I mean do you guys do this on purpos, or are you just that stupid ?If you have a red nvidia card on the desk at work, that shows nvidia is flexible in color schemes, unlike 'red 'red' red red red red red rooster cards !
You do realize you made an immense BLUNDER now, don't you ?
You thought I meant the color RED was awful.
lol
Man you people just don't have sense above a tomato.
silverblue - Friday, October 2, 2009 - link
Just because the reference cards are red, doesn't mean the manufacturers have to make them so.In fact, ASUS released a 4890 with a black PCB.
You've now descended from arguing about the length of the card and the power of its GPU to the colour of the PCB. Considering it's under a damned cooling solution, how does this matter?
engineer1 - Thursday, October 1, 2009 - link
Anand hates Nvidia because they competed against his former lover AMD, and compete against his current lover Intel. Anand you are such a rotten spoiled brat. Since this website fell into your lap you could at least make an effort to act responsibly. Have you EVER held a job working for someone else? I doubt it. And you should ban the other spoiled brats who apparently work for Microsoft and spend about 8 hours a day dominating everything posted on Dailytech such as TheIdiotNickDanger and Evil666. Bunch of Cretians.gx80050 - Friday, October 2, 2009 - link
Die painfully okay? Prefearbly by getting crushed to death in a
garbage compactor, by getting your face cut to ribbons with a
pocketknife, your head cracked open with a baseball bat, your stomach
sliced open and your entrails spilled out, and your eyeballs ripped
out of their sockets. Fucking bitch
I would love to kick you hard in the face, breaking it. Then I'd cut
your stomach open with a chainsaw, exposing your intestines. Then I'd
cut your windpipe in two with a boxcutter.
Hopefully you'll get what's coming to you. Fucking bitch
I really hope that you get curb-stomped. It'd be hilarious to see you
begging for help, and then someone stomps on the back of your head,
leaving you to die in horrible, agonizing pain. Faggot
Shut the fuck up f aggot, before you get your face bashed in and cut
to ribbons, and your throat slit.
papapapapapapapababy - Thursday, October 1, 2009 - link
lol, look at the finger, is this shoped or what! there is no card FAKE!
http://img34.imageshack.us/img34/3594/fermi1.jpg">http://img34.imageshack.us/img34/3594/fermi1.jpg