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What is gigathread?

post #1 of 3
Thread Starter 
Hey, Some 8800gts g92's on newegg list Nvidea unified gigathread as a feature. Do all the 8800gts g92's have this even though some don't list it? What the hell is gigathread?
post #2 of 3
This should clear things up for you....

Quote:
In this era of multi-core processors, I'm sure that the idea of threading isn't a new one to most of you. In CPU terms, multi-threading is a word often bandied about these days, and involves splitting an applications workload into various 'threads' to take advantage of the parallelism of dual and Quad Core CPU's - For example, in a game you could have one core for physics and one for A.I. as a basic example.

Although threading in the context of 3D rendering isn't exactly the same, the basic premise is similar - To make use of the incredible parallelism inherent in a modern GPU by effectively splitting up the workload. However, rather than splitting the workload into particular tasks or threads at a developer level, GPUs handle threading by themselves, by splitting the data to be rendered into batches of pixels which can then be sent to wherever they need to go in the GPU.

We've already mentioned the scheduler present alongside every cluster of sixteen Stream Processors - As well as this there is also a global scheduler present in G80, which oversees the graphics core as a whole. These schedulers combined together come under Nvidia's 'Gigathread' banner, and as a whole make sure that thousands of threads are 'in flight' on the graphics core at any one time to keep everything well fed. In a sense, this is similar to the concept first seen in the PC space courtesy of ATI's Radeon X1000 series 'Ultra Threaded Despatch Processor', although of course the implementation is different largely due to the presence of a Unified Shader Architecture. As part of the drive for efficiency running through Gigathread, threads can be moved between Stream Processors and clusters as required without any performance penalty, as well as elsewhere in the core as needed.

Also somewhat fitting under this section is the improved branching capabilities on show in G80. In the last generation of GPUs, we saw ATI quite often touting their large dynamic branching advantage over NVIDIA's competing hardware. Although this had little effect in even the most demanding game titles (although of course you can make a chicken and egg argument here - Was dynamic branching not used because of its poor performance on GeForce 7 series boards?), it did allow ATI to make real strides forward in the GPGPU (General Purpose GPU) segment, where the horsepower of a modern graphics board can be put to more CPU-like uses, with Stanford University's Folding@Home GPU client perhaps the most notable example of GPGPU in action. Good dynamic branching performance is a must-have for such purposes, which is why ATI have reigned supreme thus far here.

However, G80 has put NVIDIA well and truly back in the race on the dynamic branching front, thanks to a mixture of dedicated branching units in hardware to take this workload away from the Stream Processors, as well as much improved granularity - In other words, the number of pixels batched together when a branch is traversed. Granularity is important because dynamic branching is all about going through different permutations (or branches) to reach the correct result - The more pixels you send down a branch at any one time, the longer those pixels potentially have to travel to reach the correct result and thus the lower your dynamic branching performance. So, the aim is to work with as small a batch of pixels as possible when branching in this way.

For reference, ATI's R520 architecture had a dynamic branching granularity of sixteen pixels, although this was raised to forty-eight in R580 - In comparison, NVIDIA's G7x architecture had a granularity of 1024 pixels, hence its far slower performance. So, how much better is granularity in G80, I hear you ask? 16 objects for vertex data and 32 pixels for pixel data is the answer. NVIDIA are now well and truly ready to start pushing GPU-based physics and GPGPU applications on their new architecture, which should be enough to tell you that they now know they have a decent branching implementation.
 
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Hard DriveHard DriveHard DriveOptical Drive
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CoolingOSMonitorPower
Corsair H105 (Push/Pull) Windows 10 Pro x64 2x 27" Asus PG278Q ROG Swift 144hz  Corsair AX1500i Digital ATX 80 Plus Titanium 
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Lian Li PC-O8WX ATX Cube Case Logitech Z906 5.1 Surround 
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post #3 of 3
Thread Starter 
interesting...

So, is the whole list features crap just a way to sucker people into a feature all the 8800gts g92's have? If not, then, even more strange. I would bet, that if it's in that situation, the gigathread versions would have superior overclocking outcomes, due to better ordered threads. But i'm going 99.9% with it's just a feature all the cards have.

Still though, thanks for answering what it is. Sometimes, it's just better to know. lol
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