RDNA 2 deep-dive: What's inside AMD's Radeon RX 6000 graphics cards

RDNA 2. The graphics structure on the center of AMD’s kick-ass new Radeon RX 6000 graphics playing cards might sound like a easy iteration upon the unique “RDNA” GPUs that got here prior to it, however RDNA 2—which additionally powers the next-gen Xbox Sequence X and PlayStation five consoles—is a lot more than a trifling refresh. Important tweaking has ended in a shocking 54-percent build up in power-per-watt over AMD’s last-gen Radeon RX 5000 GPUs. In all probability extra particularly, the Radeon RX introduces an leading edge new “Infinity Cache” era that reimagines how reminiscence behaves in graphics playing cards. Oh, and ray tracing? AMD does that now, too.

Upload all of it up, and the Radeon RX 6800-series graphics debuting these days organize to problem Nvidia’s enthusiast-class gaming flagships for the primary time in a very long time. Head over to our Radeon RX 6800 and RX 6800 XT assessment to peer what that suggests in sensible phrases. This high-level review of the RDNA 2 structure will will let you provide an explanation for how AMD accomplished all of it. 

RDNA 2 structure adjustments

ppw AMD

AMD’s engineers approached RDNA 2 with lofty potency targets as their guiding lighting. The unique RDNA structure equipped a 50-percent performance-per-watt build up over its “GCN”-based predecessors, in any case matching Nvidia’s vaunted chronic potency, and the corporate’s executives sought after RDNA 2 to stay that tempo. Spoiler alert: They did. It took numerous onerous paintings although, in addition to shut collaboration with the Ryzen CPU structure group, as a result of RDNA 2 is constructed the use of the similar TSMC 7nm production procedure as RDNA 1. A large a part of the unique RDNA’s potency features got here from the node jump from 14nm to 7nm, however RDNA 2’s enhancements required extra really extensive tweaking.

rdna 2 arch AMD
rdna 2 compute units AMD

Regardless of the serious rejiggering, the elemental RDNA 2 construction blocks stay in large part very similar to RDNA 1’s in extensive strokes—with the exception of the addition of devoted ray accelerator hardware, which we’ll get to later—handiest scaled up a lot additional.

rdna 2 vs 1 AMD

AMD stayed modest with final era’s RDNA 1 merchandise. Its flagship, the Radeon RX 5700 XT, crowned out at 40 compute gadgets and 10.three billion transistors within its 251mm² die—a wonder making an allowance for AMD’s earlier GCN architectures scaled as much as 64 CU designs. (We’ll get to why that used to be later as smartly.) RDNA 2 blows well beyond that. The $579 Radeon RX 6800 contains 60 CUs, the $649 Radeon RX 6800 XT americathat to 72 CUs, and the flagship $999 Radeon RX 6900 XT will totally double-up final era’s RX 5700 XT with a whopping 80 CUs within an enormous 519mm² die with over 26 billion transistors. In contrast, the “Ampere” GPU die within Nvidia’s rival $1,500 GeForce RTX 3090 packs a hair over 28 billion transistors into a far higher 628mm² die.

Swiping a web page from AMD’s implausible Ryzen 5000 CPUs, RDNA 2 implements pervasive fine-grain clock gating to permit portions of the GPU to decelerate in the event that they aren’t getting used, making improvements to chronic potency. RDNA 2 moreover options extra powerful clock tree splitting and gating (like server CPUs) for a similar explanation why, however extra parallelized to hit the upper bandwidths succesful with GPUs. The corporate’s engineers additionally “aggressively” rebalanced knowledge pipelines or even redesigned whole knowledge paths, honing the structure for max potency. The ones optimizations accounted for approximately a 3rd of the as much as 54-percent performance-per-watt build up delivered within the Radeon RX 6800 and 6800 XT (and the whopping 65-percent build up promised for the flagship Radeon RX 6900 XT coming December eight).

high speed design AMD

Efficiency-per-watt isn’t all about chronic potency, although—therefore the phrase “functionality.” Some other 3rd of RDNA 2’s perf-per-watt development comes from pushing the pedal to the steel even tougher. As soon as once more, AMD’s engineers optimized the microarchitecture, common sense, and function libraries with a focal point on velocity. Probably the most tangible effects in their efforts must be the insane clock speeds of the Radeon RX 6000 GPUs. AMD’s CPU engineers have spent a very long time honing speeds at the 7nm procedure node by means of this level, they usually shared their experience with the Radeon group to nice impact.

The Radeon RX 6000-series graphics playing cards push well beyond the 2GHz barrier. Corporate representatives have been willing to tout the “unparalleled” speeds in conversations with press. They must be. All 3 high-end choices—the Radeon RX 6800, 6800 XT, and 6900 XT—have spice up clock speeds that surpass a whopping 2.1GHz. The 2 XT fashions cross the entire approach as much as 2,250MHz. The ones are below very best prerequisites, however AMD says the XT playing cards hit 2,015MHz even in gaming workloads, retaining tempo with Nvidia’s staggeringly tough Ampere GPUs, which will spice up to kind of 2GHz throughout gameplay.

AMD couldn’t have hit such rapid speeds or accomplished its chronic potency targets with out the creation of RDNA 2’s modern Infinity Cache.

RDNA 2 Infinity Cache defined

infinity cache solution AMD

RDNA 2’s standout function additionally swipes a web page from processor design—Epyc server processors, on this case. Conventional GPUs come with L1 and L2 caches of quite a lot of sizes. Radeon RX 6000 graphics playing cards upload an “Infinity Cache” that behaves in a similar fashion to the “Recreation Cache” that is helping fashionable Ryzen processors recreation such a lot higher than previous fashions did. Impressed by means of Epyc server CPUs, Infinity Cache is principally an enormous 128MB L3 cache that has been closely optimized for gaming workloads. It’s 4 occasions denser than the L3 SRAM in Epyc processors to assist make stronger chronic potency, too.

infinity cache AMD

Equipping the GPU with the sort of massive, high-speed cache shall we it stay many of the operating knowledge for any given body on-die. This protects the GPU from having to stay sending indicators the entire approach around the bundle to the 16GB of onboard GDDR6 reminiscence in lots of instances, particularly since the cache holds numerous temporal and spatial knowledge that may be reused in next frames. That makes Infinity Cache a lot quicker and a lot more power-efficient in comparison to merely expanding the bus width to the reminiscence modules.

Sam Naffziger, AMD’s product era architect, says that even if the Radeon RX 6000 GPUs stick with a modest 256-bit bus, the Infinity Cache is helping RDNA 2 ship hugely extra bandwidth-per-watt than conventional GDDR6 provided with even a humongous 512-bit bus. Through comparability, Nvidia’s rival high-end RTX 3080 and 3090 graphics playing cards make the most of wider 320-bit and 384-bit buses, respectively, paired with state of the art GDDR6X reminiscence that makes use of “PAM4” signaling era, which allows them to ship 4 imaginable values consistent with cycle, up from the standard two. That shall we GDDR6X transfer knowledge at two times the velocity of GDDR6, however with upper latency and gear calls for.

infinity cache clock speeds AMD

The Infinity Cache additionally is helping allow RDNA 2’s sky-high clock speeds. If AMD had attempted to drive the unique RDNA reminiscence subsystem on RDNA 2, Naffziger stated, it might have required a hugely higher reminiscence configuration to keep away from ravenous the GPU for bandwidth. That might have required upgrading to very large 512-bit buses, and extra, quicker reminiscence, all of which might have despatched the ability calls for skyrocketing—a no-go given RDNA 2’s design targets.

The overpowering bandwidth enabled by means of Infinity Cache helps to keep RDNA 2’s CUs amply fed, as you’ll be able to see within the chart above. When AMD’s engineers disable Infinity Cache of their labs and revert to the usual cache design with 16GB of GDDR6 reminiscence over a 256-bit bus, GPU clock frequencies fall off a cliff.

infinity cache latency AMD

Through retaining such a lot body knowledge on die, the Infinity Cache is helping the Radeon RX 6800 reasonable 34 % much less latency than the older Radeon RX 5700 XT. When a scene totally “hits” the Infinity Cache, the latency reduces additional. Naffziger says that AMD’s Infinity Cloth communique era can scale its accelerates and all the way down to optimize potency, ramping as much as 550GB/s when the Infinity Cache turns into particularly stressed out. However even if the GPU must get right of entry to your card’s precise VRAM, latency additionally improves in comparison to the last-gen Radeon playing cards because of a common velocity build up for Infinity Cloth. 

rdna 2 chip AMD

AMD tuned the Infinity Cache in this preliminary trio of enthusiast-class playing cards for 4K gaming, which is why it’s configured with an outstanding 128MB. Naffziger says the huge dimension shall we Infinity Cache succeed in a 56 % “hit charge” throughout quite a lot of titles at 4K solution, and better hit charges because the solution scales down. A part of the explanation why those playing cards carry out higher than their Nvidia festival at 1440p gaming is because of excessive Infinity Cache hit charges, AMD’s Laura Smith stated.

However the Infinity Cache functionality doesn’t scale linearly as solution decreases, Naffziger warned. Whilst you drop all the way down to 1080p, video games ceaselessly develop into extra CPU- or engine-bound than memory-bound. (I wouldn’t be shocked if extra reasonably priced Radeon RX 6000 choices one day diminished the Infinity Cache’s dimension as a result of that.)

Likewise, the Infinity Cache spreads its wings essentially the most in programs which can be extra memory-bound, although its advantages may also be felt even if a recreation must get right of entry to conventional VRAM extra ceaselessly. Naffziger says in the ones instances, RDNA 2’s general reminiscence device behaves kind of on a par with what you’d see in case you’d provided those playing cards with a 512-bit bus.

Infinity Cache very much is helping with ray tracing too.

Ray tracing with RDNA 2

Sure, AMD’s Radeon GPUs can maintain real-time ray tracing now. Nvidia kicked off the ray tracing birthday party by means of including devoted “RT cores” for dealing with ray tracing to its older RTX 20-series GPUs. Now AMD is becoming a member of the joys by means of including a unmarried devoted “ray accelerator” to each and every RDNA 2 compute unit. That implies as you progress up the Radeon RX 6000 stack, extra tough graphics playing cards with extra compute gadgets can also be higher at ray tracing, as they’ll have extra devoted ray tracing hardware.

ray tracing AMD

As you’ll be able to see in our Radeon RX 6800 and 6800 XT assessment, RDNA 2 isn’t relatively on a par with Nvidia’s second-gen ray tracing implementation. It nonetheless delivers strangely just right ray tracing functionality, reaching very playable body charges at each 1440p and 1080p solution. You received’t have the ability to play video games at 4K with the in depth lights applied sciences enabled, on the other hand, and AMD says it centered 1440p gaming as its ray tracing function. Through and big, it delivered.

Infinity Cache comes thru within the snatch right here, too. We delved deeper into how ray tracing works in our unique deep-dive of Nvidia’s Turing structure, the place the era debuted, however principally it really works by means of having devoted ray tracing hardware carry out calculations of ways the sunshine rays behave, the use of one way referred to as bounding quantity hierarchy (BVH) traversal. Appearing that job could be very memory-intensive, which is why VRAM calls for jump upward whilst you allow ray tracing in a recreation.

lkdfghpzhx 1 Nvidia

Nvidia’s BVH algorithim for ray tracing

AMD says it’s in a position to stay “an overly excessive proportion of the BVH operating set” immediately within the Infinity Cache, decreasing latency and making improvements to general functionality. The ray accelerator handles intersections within the BVH, whilst RDNA 2 makes use of usual shader code within the compute gadgets for ray transversal and shading the real scene.  

That stated, AMD does no longer have a solution for Nvidia’s Deep Finding out Tremendous Sampling (DLSS) era. Ray tracing is amazingly computationally dear, and activating it creates a putting functionality have an effect on. To counteract the loss in body charge, DLSS renders video games at a decrease solution, then upscales the overall symbol in your recreation solution the use of system finding out to spiff up the picture, all powered by means of Nvidia’s devoted AI-focused tensor cores.

Early iterations of DLSS may just appear to be Vaseline smeared in your display, however the DLSS 2.zero era rolling out in more recent video games works like black magic. It’s glorious, and really makes flipping ray tracing on much less painful. The tensor cores additionally maintain “denoising” when ray tracing is directly to keep away from a gritty glance commonplace on older, much less complex ray tracing implementations.

dx12u fidelityfx AMD

You’ll see the mysterious “Tremendous Solution” indexed right here.

AMD doesn’t come with devoted AI upscaling hardware in RDNA 2. Denoising is treated by means of the overall compute gadgets, and it really works rather well by means of my eye—however there’s no DLSS-like function to claw again misplaced frames. All over its Radeon RX 6000 disclose, AMD teased some form of DLSS rival dubbed “Tremendous Solution” as a part of its FidelityFX suite of open-source equipment with out going into element. Representatives declined to mention extra, instead of to state that Tremendous Solution will no longer be to be had instantly. That stated, as a result of AMD’s RDNA 2 powers each next-gen consoles as smartly, the corporate hopes its open-source choice finally ends up gaining traction with builders when it does arrive. The corporate’s FidelityFX toolkit additionally features a denoiser resolution that builders can put into effect.

DirectX 12 Final options and extra

However wait, there’s extra. Like Nvidia’s fresh RTX-branded GPUs, RDNA 2 is totally DirectX 12 Final-compliant. Microsoft calls DX12 “a drive multiplier for all the gaming ecosystem” by means of unifying an array of latest options—most commonly ones offered in Nvidia’s Turing-based RTX 20-series, however in large part omitted by means of builders—throughout all fashionable PC and next-gen Xbox Sequence X hardware.

variable rate shading AMD

That implies Radeon RX 6000-series graphics playing cards additionally pick out up nifty methods like mesh shading, variable charge shading, and sampler comments, which we lined in our have a look at DirectX 12 Final. All the options dangle nice attainable to make stronger each functionality and visible constancy. AMD optimized quite a lot of portions of RDNA 2 round them, comparable to making improvements to the colour compression conduct and including devoted sampler comments common sense.

AMD’s Radeon GPUs will even fortify Microsoft’s DirectStorage API when it debuts in 2021 (as will Nvidia’s RTX 30-series). DirectStorage shall we your NVMe SSD communicate immediately in your graphics card’s reminiscence for hugely advanced loading and asset-streaming functionality. Right here’s how DirectStorage targets to kill game-loading occasions at the PC. It has the possible to be an actual game-changer.

lisa su rdna 2 radeon chip AMD

Different sides of RDNA 2 won upgrades as smartly. The show engine now helps HDM1 2.1, for instance. The multi-media engine can maintain AV1 interpreting for 8K movies and features a high quality 8K HEVC encode accelerator, matching developments present in Nvidia’s Ampere GPUs. 8K is essentially the most area of interest of area of interest instances at this level, although, and that is getting lengthy sufficient.

Be sure that to take a look at our complete Radeon RX 6800 and RX 6800 XT assessment to peer how some of these RDNA 2 enhancements translate into graphics playing cards you’ll be able to in truth purchase. They’re implausible, they usually really problem Nvidia’s high-end gaming choices for the primary time since 2013’s Radeon R9 290X hit the streets. No matter else you’ll be able to say about 2020, it’s an ideal yr to be a gamer.

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