The DirectX 12 Performance Preview: AMD, NVIDIA, & Star Swarm
by Ryan Smith on February 6, 2015 2:00 PM EST- Posted in
- GPUs
- AMD
- Microsoft
- NVIDIA
- DirectX 12
CPU Scaling
Diving into our look at DirectX 12, let’s start with what is going to be the most critical component for a benchmark like Star Swarm, the CPU scaling.
Because Star Swarm is designed to exploit the threading inefficiencies of DirectX 11, the biggest gains from switching to DirectX 12 on Star Swarm come from removing the CPU bottleneck. Under DirectX 11 the bulk of Star Swarm’s batch submission work happens under a single thread, and as a result the benchmark is effectively bottlenecked by single-threaded performance, unable to scale out with multiple CPU cores. This is one of the issues DirectX 12 sets out to resolve, with the low-level API allowing Oxide to more directly control how work is submitted, and as such better balance it over multiple CPU cores.
Starting with a look at CPU scaling on our fastest cards, what we find is that besides the absurd performance difference between DirectX 11 and DirectX 12, performance scales roughly as we’d expect among our CPU configurations. Star Swarm's DirectX 11 path, being single-threaded bound, scales very slightly with clockspeed and core count increases. The DirectX 12 path on the other hand scales up moderately well from 2 to 4 cores, but doesn’t scale up beyond that. This is due to the fact that at these settings, even pushing over 100K draw calls, both GPUs are solidly GPU limited. Anything more than 4 cores goes to waste as we’re no longer CPU-bound. Which means that we don’t even need a highly threaded processor to take advantage of DirectX 12’s strengths in this scenario, as even a 4 core processor provides plenty of kick.
Meanwhile this setup also highlights the fact that under DirectX 11, there is a massive difference in performance between AMD and NVIDIA. In both cases we are completely CPU bound, with AMD’s drivers only able to deliver 1/3rd the performance of NVIDIA’s. Given that this is the original Mantle benchmark I’m not sure we should read into the DirectX 11 situation too much since AMD has little incentive to optimize for this game, but there is clearly a massive difference in CPU efficiency under DirectX 11 in this case.
Having effectively ruled out the need for 6 core CPUs for Star Swarm, let’s take a look at a breakdown across all of our cards for performance with 2 and 4 cores. What we find is that Star Swarm and DirectX 12 are so efficient that only our most powerful card, the GTX 980, finds itself CPU-bound with just 2 cores. For the AMD cards and other NVIDIA cards we can get GPU bound with the equivalent of an Intel Core i3 processor, showcasing just how effective DirectX 12’s improved batch submission process can be. In fact it’s so efficient that Oxide is running both batch submission and a complete AI simulation over just 2 cores.
Speaking of batch submission, if we look at Star Swarm’s statistics we can find out just what’s going on with batch submission. The results are nothing short of incredible, particularly in the case of AMD. Batch submission time is down from dozens of milliseconds or more to just 3-5ms for our fastest cards, an improvement just overof a whole order of magnitude. For all practical purposes the need to spend CPU time to submit batches has been eliminated entirely, with upwards of 120K draw calls being submitted in a handful of milliseconds. It is this optimization that is at the core of Star Swarm’s DirectX 12 performance improvements, and going forward it could potentially benefit many other games as well.
Another metric we can look at is actual CPU usage as reported by the OS, as shown above. In this case CPU usage more or less perfectly matches our earlier expectations: with DirectX 11 both the GTX 980 and R9 290X show very uneven usage with 1-2 cores doing the bulk of the work, whereas with DirectX 12 CPU usage is spread out evenly over all 4 CPU cores.
At the risk of speaking to the point that it’s redundant, what we’re seeing here is exactly why Mantle, DirectX 12, OpenGL Next, and other low-level APIs have been created. With single-threaded performance struggling to increase while GPUs continue to improve by leaps and bounds with each generation, something must be done to allow games to better spread out their rendering & submission workloads over multiple cores. The solution to that problem is to eliminate the abstraction and let the developers do it themselves through APIs like DirectX 12.
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eanazag - Monday, February 9, 2015 - link
Yes, and they need more millions of machines to attract developers. Find any app that exists on iOS, Android, and Windows and you'll see that the Windows version is usually lagging in support or features. Example: Star Wars Commander receives the same updates iOS does weeks later.They absolutely need developers to get on board. When they do, there should be a corresponding stream of cash flow in the Windows store.
Blessedman - Tuesday, February 10, 2015 - link
This is 100% correct... Ask any Machead if they would prefer Max Excel or Windows Excel, it is a clear choice that the windows version of Excel is far away a better product. When they can develop for an audience, do you think they would rather show off their product on the niche market (anything other than windows)?Blessedman - Tuesday, February 10, 2015 - link
Errr This isn't 100% correct.SparkySamza - Tuesday, February 10, 2015 - link
yes but numbers on mac vs mac excel, numbers wins every time cause numbers is a boss.Christopher1 - Monday, February 16, 2015 - link
True, but Windows 8 has the Store and it is a PAID upgrade from Vista and 7 so..... that comparison sorts falls flat in the real world.ymcpa - Saturday, February 7, 2015 - link
It's free only for the first year and it's not free to OEMs and large enterprise customers, who use software assurance anyways. They want everyone to upgrade to create a large enough user base to attract developers again. This will benefit windows tablets and phones and might make them competitive against ios and android. The only thing really holding tablets and phones back is the app selection. On the other hand, Google's only reason for giving away free software and service s to establish a large user so that the can sell ads to target that user base. In that scenario, you are the product.bitcrazed - Saturday, February 7, 2015 - link
"It's free only for the first year .."No. Win 10 is a free upgrade if you upgrade within a year of initial release. There is no fee to be paid after the 1st year.
Because we now live in a world where one doesn't need to replace one's machine every 3 years in order to be able to run the next OS version, Microsoft has learned that it needs to incentivize users to upgrade to newer OS' in order to prevent what happened with XP:
Although Microsoft had released Vista, 7 and 8, until fairly recently, a considerable percentage of their userbase were still running XP. Microsoft had to extend the support lifespan of XP twice to avoid leaving XP users without an upgrade path, but still they refused to upgrade. Then Microsoft could do no more and even extended support expired resulting in a larger number of upgrades from XP.
My offering Win10 as a free upgrade, Microsoft (and the entire industry) hopes to encourage users to upgrade from their current OS - XP, Vista, 7 or 8.x to the new OS sooner rather than later.
hwangeruk - Saturday, February 7, 2015 - link
Eh? His "free for the first year" comment was correct, stop splitting hairs.Microsoft is not trying to prevent what happened with XP at all, that's just wrong.
MS need apps for mobile, so wants a mass of users to get the tablet and phone space back.
They also want to win some hearts and minds as Windows 8 had a mixed reception (even though after 8.1 updates it was fine, the damage was done. Like games with launch issues sometimes don't recover from negative early reviews)
This has 0 to do with XP, and the XP extended support for only for paying customers not generally consumers. This move has 0 to do with XP, you are so wrong on that.
zodiacfml - Sunday, February 8, 2015 - link
It is free. They put it for free for the first year of the OS so that people are forced to upgrade immediately and not any amount of time longer than that as it that defeats the purpose of putting a huge percentage of people into just one, current operating system.Besides, adopters would be will beta testers with little obligation from MS.
Wwhat - Sunday, February 8, 2015 - link
But what does windows10 desktop to do with getting the tablet and phone space? And what do you mean with "get the tablet and phone space back", back? MS never had that market ever, nor is MS likely to get it.But yes, they are likely hoping to gain from 'an appstore' and 'cloud' and the always listening and handy for advertisers and security services alike voice-command thing.
All of which exemplifies the reason to worry..