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RDNA 3
RDNA 3 is a GPU microarchitecture designed by AMD, released with the Radeon RX 7000 series on December 13, 2022. Alongside powering the RX 7000 series, RDNA 3 is also featured in the SoCs designed by AMD for the Asus ROG Ally, Lenovo Legion Go, and the PlayStation 5 Pro consoles.
On June 9, 2022, AMD held their Financial Analyst Day where they presented a client GPU roadmap which contained mention of RDNA 3 coming in 2022 and RDNA 4 coming in 2024. AMD announced to investors their intention to achieve a performance-per-watt uplift of over 50% with RDNA 3 and that the upcoming architecture would be built using chiplet packaging on a 5 nm process.
A sneak preview for RDNA 3 was included towards the end of AMD's Ryzen 7000 unveiling event on August 29, 2022. The preview included RDNA 3 running gameplay of Lies of P, AMD CEO Lisa Su confirming that a chiplet design would be used, and a partial look at AMD's reference design for an RDNA 3 GPU.
Full details for the RDNA 3 architecture were unveiled on November 3, 2022 at an event in Las Vegas.
For the first time ever in a consumer GPU, RDNA 3 utilizes modular chiplets rather than a single large monolithic die. AMD previously had great success with its use of chiplets in its Ryzen desktop and Epyc server processors. The decision to move to a chiplet-based GPU microarchitecture was led by AMD Senior Vice President Sam Naffziger who had also lead the chiplet initiative with Ryzen and Epyc. The development of RDNA 3's chiplet architecture began towards the end of 2017 with Naffziger leading the AMD graphics team in the effort. The benefit of using chiplets is that dies can be fabricated on different process nodes depending on their functions and intended purpose. According to Naffziger, cache and SRAM do not scale as linearly as logic does on advanced nodes like N5 in terms of density and power consumption so they can instead be fabricated on the cheaper, more mature N6 node. The use of smaller dies rather than one large monolithic die is beneficial for maximizing wafer yields as more dies can be fitted onto a single wafer. Alternatively, a large monolithic RDNA 3 die built on N5 would be more expensive to produce with lower yields.
RDNA 3 uses two types of chiplets: the Graphics Compute Die (GCD) and Memory Cache Dies (MCDs). On Ryzen and Epyc processors, AMD used its PCIe-based Infinity Fabric protocol with the package's dies connected via traces on an organic substrate. This approach is easily scalable in a cost-effective manner but has the drawbacks of increased latency, increased power consumption when moving data between dies at around 1.5 picojoules per bit, and it cannot achieve the connection density needed for high-bandwidth GPUs. An organic package could not host the number of wires that would be needed to connect multiple dies in a GPU.
RDNA 3's dies are instead connected using TSMC's Integrated Fan-Out Re-Distribution Layer (InFO-RDL) packaging technique which provides a silicon bridge for high bandwidth and high density die-to-die communication. InFO allows dies to be connected without the use of a more costly silicon interposer such as the one used in AMD's Instinct MI200 and MI300 datacenter accelerators. Each Infinity Fanout link has 9.2 Gbps in bandwidth. Naffziger explains that "The bandwidth density that we achieve is almost 10x" with the Infinity Fanout rather than the wires used by Ryzen and Epyc processors. The chiplet interconnects in RDNA achieve cumulative bandwidth of 5.3 TB/s.
With a respective 2.05 billion transistors, each Memory Cache Die (MCD) contains 16 MB of L3 cache. Theoretically, additional L3 cache could be added to the MCDs via AMD's 3D V-Cache die stacking technology as the MCDs contain unused TSV connection points. Also present on each MCD are two physical 32-bit GDDR6 memory interfaces for a combined 64-bit interface per MCD. The Radeon RX 7900 XTX has a 384-bit memory bus through the use of six MCDs while the RX 7900 XT has a 320-bit bus due to its five MCDs.
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RDNA 3 AI simulator
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RDNA 3
RDNA 3 is a GPU microarchitecture designed by AMD, released with the Radeon RX 7000 series on December 13, 2022. Alongside powering the RX 7000 series, RDNA 3 is also featured in the SoCs designed by AMD for the Asus ROG Ally, Lenovo Legion Go, and the PlayStation 5 Pro consoles.
On June 9, 2022, AMD held their Financial Analyst Day where they presented a client GPU roadmap which contained mention of RDNA 3 coming in 2022 and RDNA 4 coming in 2024. AMD announced to investors their intention to achieve a performance-per-watt uplift of over 50% with RDNA 3 and that the upcoming architecture would be built using chiplet packaging on a 5 nm process.
A sneak preview for RDNA 3 was included towards the end of AMD's Ryzen 7000 unveiling event on August 29, 2022. The preview included RDNA 3 running gameplay of Lies of P, AMD CEO Lisa Su confirming that a chiplet design would be used, and a partial look at AMD's reference design for an RDNA 3 GPU.
Full details for the RDNA 3 architecture were unveiled on November 3, 2022 at an event in Las Vegas.
For the first time ever in a consumer GPU, RDNA 3 utilizes modular chiplets rather than a single large monolithic die. AMD previously had great success with its use of chiplets in its Ryzen desktop and Epyc server processors. The decision to move to a chiplet-based GPU microarchitecture was led by AMD Senior Vice President Sam Naffziger who had also lead the chiplet initiative with Ryzen and Epyc. The development of RDNA 3's chiplet architecture began towards the end of 2017 with Naffziger leading the AMD graphics team in the effort. The benefit of using chiplets is that dies can be fabricated on different process nodes depending on their functions and intended purpose. According to Naffziger, cache and SRAM do not scale as linearly as logic does on advanced nodes like N5 in terms of density and power consumption so they can instead be fabricated on the cheaper, more mature N6 node. The use of smaller dies rather than one large monolithic die is beneficial for maximizing wafer yields as more dies can be fitted onto a single wafer. Alternatively, a large monolithic RDNA 3 die built on N5 would be more expensive to produce with lower yields.
RDNA 3 uses two types of chiplets: the Graphics Compute Die (GCD) and Memory Cache Dies (MCDs). On Ryzen and Epyc processors, AMD used its PCIe-based Infinity Fabric protocol with the package's dies connected via traces on an organic substrate. This approach is easily scalable in a cost-effective manner but has the drawbacks of increased latency, increased power consumption when moving data between dies at around 1.5 picojoules per bit, and it cannot achieve the connection density needed for high-bandwidth GPUs. An organic package could not host the number of wires that would be needed to connect multiple dies in a GPU.
RDNA 3's dies are instead connected using TSMC's Integrated Fan-Out Re-Distribution Layer (InFO-RDL) packaging technique which provides a silicon bridge for high bandwidth and high density die-to-die communication. InFO allows dies to be connected without the use of a more costly silicon interposer such as the one used in AMD's Instinct MI200 and MI300 datacenter accelerators. Each Infinity Fanout link has 9.2 Gbps in bandwidth. Naffziger explains that "The bandwidth density that we achieve is almost 10x" with the Infinity Fanout rather than the wires used by Ryzen and Epyc processors. The chiplet interconnects in RDNA achieve cumulative bandwidth of 5.3 TB/s.
With a respective 2.05 billion transistors, each Memory Cache Die (MCD) contains 16 MB of L3 cache. Theoretically, additional L3 cache could be added to the MCDs via AMD's 3D V-Cache die stacking technology as the MCDs contain unused TSV connection points. Also present on each MCD are two physical 32-bit GDDR6 memory interfaces for a combined 64-bit interface per MCD. The Radeon RX 7900 XTX has a 384-bit memory bus through the use of six MCDs while the RX 7900 XT has a 320-bit bus due to its five MCDs.