RDNA (microarchitecture)

RDNA (Radeon DNA[2][3]) is the codename for a GPU microarchitecture and accompanying instruction set developed by AMD. It is the successor to their Graphics Core Next (GCN) microarchitecture/instruction set. The first product lineup featuring RDNA was the Radeon RX 5000 series of video cards, launched on July 7, 2019.[1][4] The architecture is also planned to be used in mobile products and the PlayStation 5 and Xbox Series X game consoles, both of which will use RDNA2-based graphics.[5]

AMD RDNA 1
Release dateJuly 7, 2019 (July 7, 2019)[1]
Fabrication processTSMC 7 nm
History
PredecessorGraphics Core Next 5
SuccessorRDNA 2
A generic block diagram of a GPU.

It is likely to be RISC SIMD (or rather SIMT) microarchitecture. It is manufactured and fabricated with TSMC's 7 nm FinFET graphics chips used in the Navi series of AMD Radeon graphics cards.[6]

Architecture

The architecture features a new processor design, although the first details released at AMD's Computex keynote hints at aspects from the previous a Graphics Core Next (GCN) architecture being present. It will feature multi-level cache hierarchy and an improved rendering pipeline, with support for GDDR6 memory. A completely redesigned (non-hybrid) architecture is planned as a successor (rumor).[7]

Starting with the architecture itself, one of the biggest changes for RDNA is the width of a wavefront, the fundamental group of work. GCN in all of its iterations was 64 threads wide, meaning 64 threads were bundled together into a single wavefront for execution. RDNA drops this to a native 32 threads wide. At the same time, AMD has expanded the width of their SIMDs from 16 slots to 32 (aka SIMD32), meaning the size of a wavefront now matches the SIMD size.[8]

RDNA also introduces working primitive shaders. While the feature was present in the hardware of the Vega architecture, it was difficult to get a real-world performance boost from and thus AMD never enabled it. Primitive shaders in RDNA are compiler-controlled.[8]

The display controller in RDNA has been updated to support Display Stream Compression 1.2a, allowing output in 4k@240 Hz, HDR 4K@120 Hz, and HDR 8K@60 Hz.[8][9]

Instruction set
Main article: Graphics Core Next: Instruction set

AMD's GPUOpen website hosts a PDF document aiming to describe the environment, the organization and the program state of AMD “RDNA” Generation devices. It details the instruction set and the microcode formats native to this family of processors that are accessible to programmers and compilers.[10]

The RDNA instruction set is owned by AMD (that also owns the X86-64 instruction set).

Differences between GCN and RDNA 1

There are architectural changes which affect how code is scheduled:

  1. Single cycle instruction issue:
    • GCN issued one instruction per wave once every 4 cycles.
    • RDNA issues instructions every cycle.
  2. Wave32:
    • GCN used a wavefront size of 64 threads (work items).
    • RDNA supports both wavefront sizes of 32 and 64 threads.
  3. Workgroup Processors:
    • GCN grouped the shader hardware into "compute units" (CUs) which contained scalar ALUs and vector ALUs, LDS and memory access. One CU contains 4 SIMD16s which share one path to memory.
    • RDNA introduced the "workgroup processor" ("WGP"). The WGP replaces the compute unit as the basic unit of shader computation hardware/computing. One WGP encompasses 2 CUs. This allows significantly more compute power and memory bandwidth to be directed at a single workgroup. In RDNA 1 CU is one half of a WGP.

RDNA 2
AMD RDNA 2
Fabrication processTSMC "Enhanced" 7nm
History
PredecessorRDNA 1

RDNA 2[11] (also RDNA2[12]) is the successor to the RDNA 1 microarchitecture and is planned to be released in 2020.[12][13] According to statements from AMD, RDNA 2 will be a "refresh" of the RDNA 1 architecture.[14]

More information about RDNA 2 was made public on AMD's Financial Analyst Day on March 5th, 2020.[15][13][16] AMD claims it will provide a 50% performance-per-watt improvement over RDNA 1 and, although no exact figures were provided yet, increases in clock speed and instructions-per-clock.[17] Additional features confirmed by AMD include real-time, hardware accelerated ray tracing and variable rate shading.[17] RDNA 2 will be used in next-generation gaming consoles and PC graphics cards[17] code-named "Navi 2X".[18]

Usage in ninth-generation gaming consoles

RDNA 2 has been confirmed as the graphics microarchitecture that will be used in the upcoming ninth-generation gaming consoles (namely Xbox Series X[19] from Microsoft, and PlayStation 5[20] from Sony), with proprietary tweaks and different GPU configurations in each systems' implementation.

See also

References
  1. AMD press release: "AMD Announces Next-Generation Leadership Products at Computex 2019 Keynote". AMD.com. Retrieved October 5th, 2019
  2. Smith, Ryan (26 May 2019). "Home> GPUs AMD Teases First Navi GPU Products: RX 5700 Series Launches in July, 25% Improved Perf-Per-Clock". AnandTech. Retrieved 21 June 2019.
  3. "AMD RDNA Architecture".
  4. AMD launches RX 5700 XT and RX 5700 GPUs with RDNA architecture
  5. Smith, Ryan (10 June 2019). "GPUs AMD Announces Radeon RX 5700 XT & RX 5700: The Next Gen of AMD Video Cards Starts on July 7th At $449/$379". AnandTech. p. 1. Retrieved 21 June 2019.
  6. "AMD Radeon RX 5700 XT release date, price, specs, and performance". PCGamesN. Retrieved 28 June 2019.
  7. "AMD Radeon RX 5000 With Navi GPUs A Hybrid of RDNA & GCN Chip Architecture – Pure RDNA Based 'Navi 20' GPU Coming in 2020".
  8. Smith, Ryan (10 June 2019). "GPUs AMD Announces Radeon RX 5700 XT & RX 5700: The Next Gen of AMD Video Cards Starts on July 7th At $449/$379". AnandTech. p. 2. Retrieved 21 June 2019.
  9. Stobing, Chris (10 June 2019). "AMD Details Radeon RX 5700 'Navi' GPUs: Here's What You Need to Know". PC Magazine. Ziff Davis, LLC. Retrieved 21 June 2019.
  10. "AMD RDNA 1.0 Instruction Set Architecture". GPUOpen.
  11. "AMD Investor Relations presention (PDF)". AMD.com. Advanced Micro Devices. 2019. Retrieved 2020-02-08.
  12. "Navi Refresh and RDNA2 Both In 2020, According to AMD". anandtech.com. AnandTech. 2020-01-28. Retrieved 2020-02-08.
  13. "AMD 'Big Navi' GPU might be right around the corner – but don't hold your breath". techradar.com. TechRadar. 2020-02-03. Retrieved 2020-02-08.
  14. "AMD to Introduce New Next-Gen RDNA GPUs in 2020, Not a Typical 'Refresh' of Navi". tomshardware.com. Tom's Hardware. 2020-01-29. Retrieved 2020-02-08.
  15. "AMD will unveil RDNA 2 graphics cards on March 5". pcgamesn.com. PCGamesN. 2020-01-29. Retrieved 2020-02-08.
  16. March 2020, Paul Alcorn 05. "AMD Financial Analyst Day 2020: CPU and GPU Roadmaps, X3D Die Stacking Revealed". Tom's Hardware. Retrieved 2020-03-07.
  17. Smith, Ryan. "AMD's RDNA 2 Gets A Codename: "Navi 2X" Comes This Year With 50% Improved Perf-Per-Watt". www.anandtech.com. Retrieved 2020-03-07.
  18. Smith, Ryan. "AMD's RDNA 2 Gets A Codename: "Navi 2X" Comes This Year With 50% Improved Perf-Per-Watt". www.anandtech.com. Retrieved 2020-03-16.
  19. Smith, Ryan. "Microsoft Drops More Xbox Series X Tech Specs: Zen 2 + RDNA 2, 12 TFLOPs GPU, HDMI 2.1, & a Custom SSD". www.anandtech.com. Retrieved 2020-03-19.
  20. "Unveiling New Details of PlayStation 5: Hardware Technical Specs [UPDATED]". PlayStation.Blog. 2020-03-18. Retrieved 2020-03-19.
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