Seems a bit old not to be on SW but perhaps I missed it and if so, go ahead and sue me then lock the thread. :P
Basically teh TLDR is...
Very interesting and if all on the up & up, one can understand how mooaar percieved brute powah doesn't really mean more powerful games. :cool:
Long read so I'll just post some tidbits, full story, hit the link.
Some of the story.
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http://www.eurogamer.net/articles/digitalfoundry-vs-the-xbox-one-architects
Digital Foundry vs. the Xbox One architects
"There's a lot of misinformation out there and a lot of people who don't get it. We're actually extremely proud of our design."
( starts like this)
Two months away from the release of the next generation consoles, many have already made up their minds about which machine offers more gaming power before a single game has been released. Compare basic graphics and memory bandwidth specs side-by-side and it looks like a wash - PlayStation 4 comprehensively bests Xbox One to such a degree that sensible discussion of the respective merits of both consoles seems impossible. They're using the same core AMD technologies, only Sony has faster memory and a much larger graphics chip. But is it really that simple?
In the wake of stories from unnamed sources suggesting that PS4 has a significant advantage over its Xbox counterpart, Microsoft wanted to set the record straight. Last Tuesday, Digital Foundry dialled into a conference call to talk with two key technical personnel behind the Xbox One project - passionate engineers who wanted the opportunity to put their story across in a deep-dive technical discussion where all the controversies could be addressed. Within moments of the conversation starting, it quickly became clear that balance would be the theme.
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(some in the midle )
GPU Compute and the importance of the CPU
Goosen also believes that leaked Sony documents on VGLeaks bear out Microsoft's argument:
"Sony was actually agreeing with us. They said that their system was balanced for 14 CUs. They used that term: balance. Balance is so important in terms of your actual efficient design. Their additional four CUs are very beneficial for their additional GPGPU work. We've actually taken a very different tack on that. The experiments we did showed that we had headroom on CUs as well. In terms of balance, we did index more in terms of CUs than needed so we have CU overhead. There is room for our titles to grow over time in terms of CU utilisation."
Microsoft's approach to asynchronous GPU compute is somewhat different to Sony's - something we'll track back on at a later date. But essentially, rather than concentrate extensively on raw compute power, their philosophy is that both CPU and GPU need lower latency access to the same memory. Goosen points to the Exemplar skeletal tracking system on Kinect on Xbox 360 as an example for why they took that direction.
"Exemplar ironically doesn't need much ALU. It's much more about the latency you have in terms of memory fetch, so this is kind of a natural evolution for us," he says. "It's like, OK, it's the memory system which is more important for some particular GPGPU workloads."
The team is also keen to emphasise that the 150MHz boost to CPU clock speed is actually a whole lot more important than many believe it is.
"Interestingly, the biggest source of your frame-rate drops actually comes from the CPU, not the GPU," Goosen reveals. "Adding the margin on the CPU... we actually had titles that were losing frames largely because they were CPU-bound in terms of their core threads. In providing what looks like a very little boost, it's actually a very significant win for us in making sure that we get the steady frame-rates on our console."
This in part explains why several of the custom hardware blocks - the Data Move Engines - are geared towards freeing up CPU time. Profiling revealed that this was a genuine issue, which has been balanced with a combination of the clock speed boost and fixed function silicon - the additional processors built in to the Xbox One processor.
"We've got a lot of CPU offload going on. We've got the SHAPE, the more efficient command processor relative to the standard design, we've got the clock boost - it's in large part actually to ensure that we've got the headroom for the frame-rates," Goosen continues - but it seems that the systems's Data Move Engines can help the GPU too.
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(ends with this)
"Imagine you've rendered to a depth buffer there in ESRAM. And now you're switching to another depth buffer. You may want to go and pull what is now a texture into DDR so that you can texture out of it later, and you're not doing tons of reads from that texture so it actually makes more sense for it to be in DDR. You can use the Move Engines to move these things asynchronously in concert with the GPU so the GPU isn't spending any time on the move. You've got the DMA engine doing it. Now the GPU can go on and immediately work on the next render target rather than simply move bits around."
Other areas of custom silicon are also designed to help out the graphics performance.
"We've done things on the GPU side as well with our hardware overlays to ensure more consistent frame-rates," Goosen adds. "We have two independent layers we can give to the titles where one can be 3D content, one can be the HUD. We have a higher quality scaler than we had on Xbox 360. What this does is that we actually allow you to change the scaler parameters on a frame-by-frame basis."
Dynamic resolution scaling isn't new - we've seen it implemented on a lot of current-gen titles. Indeed, the first example in the current generation was on a Sony title: WipEout HD. Impact on image quality can be rough at 720p, but at higher resolutions and in concert with superior scaling, it could be a viable performance equalising measure.
"I talked about CPU glitches causing frame glitches... GPU workloads tend to be more coherent frame to frame. There doesn't tend to be big spikes like you get on the CPU and so you can adapt to that," Goosen explains.
"What we're seeing in titles is adopting the notion of dynamic resolution scaling to avoid glitching frame-rate. As they start getting into an area where they're starting to hit on the margin there where they could potentially go over their frame budget, they could start dynamically scaling back on resolution and they can keep their HUD in terms of true resolution and the 3D content is squeezing. Again, from my aspect as a gamer I'd rather have a consistent frame-rate and some squeezing on the number of pixels than have those frame-rate glitches."
"From a power/efficiency standpoint as well, fixed functions are more power-friendly on fixed function units," adds Nick Baker. "We put data compression on there as well, so we have LZ compression/decompression and also motion JPEG decode which helps with Kinect. So there's a lot more to the Data Move Engines than moving from one block of memory to another."
We've been talking in-depth for over an hour and our time draws to a close. The entire discussion has been completely tech-centric, to the point where we'd almost forgotten that the November launch of Xbox One is likely to be hugely significant for Nick Baker and Andrew Goosen personally. How does it feel to see the console begin to roll off the production line after years in development?
"Yeah, getting something out is always, always a great feeling [but] my team work on multiple programs in parallel - we're constantly busy working on the architecture team," says Baker.
Goosen has the final word:
"For me, the biggest reward is to go and play the games and see that they look great and that yeah, this is why we did all that hard work. As a graphics guy it's so rewarding to see those pixels up on the screen."
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