If im wrong, feel free to correct me though!
Well, that's kinda what he is saying, he's just asking if it was possible to have it double / how it could be possible.Originally Posted by ColdBlooder
Not sure but if i remember correctly, in SLI/Crossfire the ram is mirrored, not doubled. So with 2 3gb cards in crossfire you still have 3gb for games. Just both cards having the same content in the memory.
If im wrong, feel free to correct me though!
You just read the thread title and not the OP, didn't you? ;)Originally Posted by ColdBlooder
Not sure but if i remember correctly, in SLI/Crossfire the ram is mirrored, not doubled. So with 2 3gb cards in crossfire you still have 3gb for games. Just both cards having the same content in the memory.
If im wrong, feel free to correct me though!
Older gpus like the voodoo sli cards I think rendered half of each frame (one horizontal line in turns I believe).
Which then also had the advantage of not having uneven frametimes (microstutter) or extra frames of vsync input lag.
So either you are bandwidth starved or you get the garbage laggy uneven framerate crap that you get today, sli is just a bad idea full stop.
if the full RAM pool would be available to both GPUs on both cards, then the GPU on card 1 would need to access the RAM on card 2 over the PCI-E lanes, which is infinitely slower than having the RAM on the PCB of the card itself and would thus completely destroy GPU performance
theoretically a super low latency, high bandwidth SLI/Xfire bridge could help, but that seems about as realistic as low latency Cloud Processing ...
Complete mobo redesign.
Dont really understand OP is it because of the 8GB of gddr5?
Because i don't see devs using that on the pc ports given how the X1 works with ddr3.
Bandwidth also need to be shared between the cpu and gpu on ps4.
GPU already have faster bandwidth then the ps4. Devs just need to make use of a streaming engine for the pc port.
Well i dont think its possible cause every gpu renders half of the same frame so they basically need to have the same data to access too. And also a big issue:Well, that's kinda what he is saying, he's just asking if it was possible to have it double / how it could be possible.
Latency.
If the gpu1 needs something from ram pool 2, the latency and "wait" for the data to arrive will propably slow the performance alot.
Where the hell is he talking about PS4 or XB1?Originally Posted by dragonelite
You need a fast shared pool of ram maybe 3D ddr4 is the solution for that for what you want OP.
Dont really understand OP is it because of the 8GB of gddr5?
Because i don't see devs using that on the pc ports given how the X1 works with ddr3.
Bandwidth also need to be shared between the cpu and gpu on ps4.
GPU already have faster bandwidth then the ps4. Devs just need to make use of a streaming engine for the pc port.
It simply doesn't really work. Actually, the more we get into complex, custom GPU compute programs, the less traditional SLI or crossfire (with driver-managed card-level parallelism) makes sense. It has always been a huge waste of resources, but now you could be looking at adding lots of per-game inter-frame dependencies into the mix.Originally Posted by cobragt4001
Only reason I decided to make this topic is I would like to know what actually keeps us from gaining extra vram when we decide to go sli or crossfire by getting another card. I understand why as of now why we can't double up on ram with videocards the way they are and how sli and crossfire works, one gpu renders even frames, the other renders odd frames and the vram is simply cloned. What would AMD or nvidia have to do to actually make multigpu setups actually double up, or triple up in the total vram pool? Would pci 3 be fast enough to actually make multigpus double up in vram or is it software that was to be changed or a combination of needed software and hardware? I thought it would be interesting to discuss this
The good news is, with the increase in GDDR5 densities, it's really not that hard to get more than sufficient quantities of memory onto a single card.
These are a couple reasons simplified, hopefully it answers your question.
How does this work for single card sli/xfire solutions, like the GTX690/HD7990?
Do they double the ram for mirroring or don't they need to do that since both gpu's are on the same board?
"Single-card" SLI / Crossfire works exactly like normal, if it's two 2GB cards, it's still a 2GB card.Interesting topic.
How does this work for single card sli/xfire solutions, like the GTX690/HD7990?
Do they double the ram for mirroring or don't they need to do that since both gpu's are on the same board?
Short answer: nothing.Originally Posted by cobragt4001
Only reason I decided to make this topic is I would like to know what actually keeps us from gaining extra vram when we decide to go sli or crossfire by getting another card. I understand why as of now why we can't double up on ram with videocards the way they are and how sli and crossfire works, one gpu renders even frames, the other renders odd frames and the vram is simply cloned. What would AMD or nvidia have to do to actually make multigpu setups actually double up, or triple up in the total vram pool? Would pci 3 be fast enough to actually make multigpus double up in vram or is it software that was to be changed or a combination of needed software and hardware? I thought it would be interesting to discuss this
Interleaving memory across the cards would eliminate mirrored data. So every time the GPU reads a kilobyte worth of textures or whatevs, half of it would come from its own memory, and the other half from the "remote" GPU.
Memory interleaving is a great technique when all memory pools are the same speed. You effectively multiply bandwidth by the amount of channels with little if any drawbacks (all contemporary "dual-channel" memory controllers in CPUs work this way). And you still get to use 100% of the storage, with no duplication.
Something like this is definitely technically feasible on GPUs, but prohibitively slow. PCIe 3.0 still only transfers 16GB/s. Local memory is 10x+ faster. Interleaving a local pool and a pool accessed through PCIe would effectively slow down all GPU memory access to the slower of the two pools. You'd get the equivalent of saddling a modern GPU with DDR3-1066 on a 128 bit bus.
Oh all right, but how do they fit that all on a single board?Oh no, if they are advertised as 4GB, it just means there's two 4GB cards stuck together. Just like a normal SLI / Crossfire setup.
I thought PS4 was so shocking, because they used 512MB ram blocks, since it wouldn't fit otherwise. I do understand the board of the PS4 is hardly comparable to a separate GPU board.
So that does that mean you could have single card GPU with 8GB with 256MB ram block?
Ah so confusing. X.xyeah a GTX690 will only have 2 GB of RAM available
well all respectable Dutch shops put "4 GB" in their technical descriptionWait, they advertise it as 4GB? Man, I didn't know that :|
hell if you look at the Asus 690 , it's actually called "GTX690-4GD5" ... wonder what the 4 refers too :)
edit: ha from the Asus site
where's the beef !? ;DASUS GTX 690: dual-GPU power enters the 28nm generation
The world's fastest graphics card with a dual-GPU and beefy 4GB GDDR5 memory