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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Zingam - Thursday, October 1, 2009 - link
Perhaps next gen consoles would be C++ based and not API based (what a great terminology). So in that sense DirectX won't matter like it won't matter on Larrabee because it will be emulated in software. Larrabee would not have any silicon dedicated to OpenGL or DirectX I think.Once GPUs get fast enough I guess they won;t be called Graphics processors anymore and will support APIs as software implementations.
marc1000 - Thursday, October 1, 2009 - link
well, perhaps... I was searching the web yesterday for info on the new consoles, it was kinda sad. if we do not get a new minimun-standard (a powerful console), then the PC games will not be that hard to run on PCs... then my old Radeon 3850 is still capable of running almost ALL games with "good enough" permformance (read: average 30-50fps on most of the console ports to PC).and so: no reason to upgrade! :-(
Dobs - Wednesday, September 30, 2009 - link
Personally I think Eyefinity will be remembered as the master stroke as well as first to implement DirectX 11. Nvidia may get 10 fps more in DirectX 11 in Q2 2010 but will still struggle until it has it's own version of Eyefinity.Current uber-cool for the cashed-up is Eyefinity and once you have 3 or 6 monitors you will only buy hardware that will support it. These 'cashed-up' PC gamers are usually Nvidia's favorite customers.
Nvidia needs flexible wrap-around OLED mega resolution monitors to come out yesterday, but I'm pretty sure that didn't happen... 5850 which supports 3 monitors came out yesterday. :P
SiliconDoc - Thursday, October 1, 2009 - link
Nvidia has supported FOUR monitors on say for instance, the 570i sli, for like YEARS dude.Just put in 2 nv cards, plug em up - and off you go, it's right in the motherboard manuals...
Heck you can plug in two ati cards for that matter.
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Anyway on the triple monitor with this 5870/50, the drivers are a mess, some having found the patch won't be for a month, then the extra $100 cable is needed, too, as some have mentioned, that ati has not included.
They're pissed.
Dobs - Thursday, October 1, 2009 - link
I'll be avoiding the extra $100 cable by getting DisplayPort monitors from the start. Also want to get ips monitor (i think) so that it will support the portrait mode.If I already had 3 non-DisplayPort monitors, I wouldn't mind shelling out for the DisplayPort adapter if that was my only expense. But if the adapter was flakey I'd be upset as well. I know multi-monitors have been around for years, but they've never been this easy to set-up... Even I could do it :P And the drivers will get better in time, and no doubt future games will look to include Eyefinity as well.
SiliconDoc - Thursday, October 1, 2009 - link
Well I do hope you have good luck and that you and your son enjoy it ( no doubt will if you manage get it), and it would be nice if you can eventually link a pic (likely in some future article text area) just because.I think eyefinity has an inherent advantage, cheaper motherboard possible, 3 on one card, and with 3 from the same card, you can have the concave wrap view going with easy setup.
I agree however with the comment that it won't be a widely used feature, and realize most don't even use both monitor hookups on their videocards that are already available as standard, since long ago, say the 9600se and before.
(I use two though, and I have to say it is a huge difference, and much, much better than one)
yacoub - Wednesday, September 30, 2009 - link
Wake up: 99% of people don't give a crap about Eyefinity. Not only do the VAST, VAST majority of customers have just one display, but those who do have multiple ones (like myself) often have completely different displays, not multiple of the same model and size. And then, even when you find that 0.1% of the customer base that has two or more identical monitors side-by-side, you have to find the ones who game on them. Then of those people, find the ones who actually WANT to have their game screen split across two monitors with a thick line of two display borders right in the middle of their image.Eyefinity is relevant to such an infinitesimally small number of people it is laughable every time someone mentions it like it's some sort of "killer app" feature.
Jamahl - Thursday, October 1, 2009 - link
thats why eyefinity has millions of youtube views already right.yacoub - Thursday, October 1, 2009 - link
because purchases are measured in YouTube views. wow, just... wow.ClownPuncher - Thursday, October 1, 2009 - link
It clearly means people are interested enough to look. Wow, just...wow.You don't like it, other people do. Get over it.