AMD RDNA 5 Secret Sauce Unveiled? Improved Dual-Issue could double performance
AMD LLVM patch unveils HUGE improvement for RDNA 5 graphics cards
A new LLVM patch from AMD for its gfx1310 (RDNA 5) graphics architecture has unveiled some of the secret sauce behind AMD’s next-generation graphics cards. Through a feature called “Dual Issue”, two operations can be completed during a single clock cycle, doubling the performance of affected workloads.
With RDNA 5, new instructions should enable dual issue across a range of workloads, effectively doubling AMD’s computational performance. While Dual Issue has been a part of AMD’s RDNA graphics architectures since RDNA 3, the feature has not been that useful for many users, especially gamers. With broader instruction support and fewer restrictions, RDNA 5 should address these issues.
Dual Issue VALU is a feature implemented in the RDNA 3 architecture (GFX11) that allows simultaneous issuance of up to two types
VOPDof system instructions ( ) to both the X and Y sides. However, the number of supported instructions is limited, and some instructions can only be selected on the Y side. There are also several conditions, such as the fact that it is only supported in Wave32 mode and that separate register banks must be used for the X and Y sides to avoid register bank conflicts.V_DUAL_*RDNA 5 (gfx1310)
VOPDadded instructions such asV_{MAX,MIN}_I32_e32, V_SUB_U32_e32, V_LSHRREV_B32_e32, V_ASHRREV_I32_e32extracting the maximum and minimum values of integers, subtraction instructions, and bit shift instructions.
On the other hand, bitwise AND instructionsV_AND_B32were removed.
What started with RDNA 3 should become useful with RDNA 5
AMD’s earlier Dual Issue implementations have been problematic. It only worked with a small number of instructions and needed Wave32 mode to function. In simple terms, Dual Issue support existed, but it wasn’t a useful feature for most users. It looks like AMD plans to change that with RDNA 5.
With AMD’s older implementation, most workloads did not benefit from AMD’s hardware-level Dual Issue support. With RDNA 5, new instructions like V_{MAX,MIN}_I32_e32, V_SUB_U32_e32, V_LSHRREV_B32_e32, V_ASHRREV_I32_e32e, and the ability to use the same input registers for X and Y tiles increase the usability of Dual Issue. In other words, AMD is making Dual Issue more useful by removing some of its prior limitations while increasing the number of workloads that can benefit from it.
It’s worth noting that Sony opted to exclude Dual Issue support from its PlayStation 5 Pro consoles due to these challenges. The PS5 Pro uses a hybrid AMD GPU architecture that features elements of RDNA 2 and newer graphics architectures. While Dual Issue mode can double the system’s peak TFLOPS, the difficulty in accessing this performance made it a no-go for Sony. Developers couldn’t easily benefit from these potential gains, making the feature unsuitable for its enhanced PS5 console. With RDNA 5, gamers and developers will be able to access more of AMD’s maximum potential computational performance.
Furthermore, RDNA 5 (gfx1310) has partially relaxed the limitations in Dual Issue, allowing the same input register to be specified for both the X and Y sides, which will also help increase the number of cases in which Dual Issue can be used.
Dual Issue is part of the secret sauce that makes RDNA 5 special, though console support is key
With RDNA 5, AMD is making it easier for software developers to access the peak theoretical computational performance of its graphics cards. With RDNA 5 being the graphics architecture behind both the PlayStation 6 and Xbox Project Helix (leaked specifications here), game developers will be encouraged to optimise their game workloads for this architecture to improve performance. This one-two punch is what should make Dual Issue a killer feature for AMD’s RDNA 5 graphics architecture. For all prior RDNA architectures, Dual Issue was difficult to utilise and lacked console buy-in. That changes with RDNA 5.
Until RDNA 5 launches, developers have no reason to cater their workloads to AMD’s Dual Issue implementation. After all, AMD’s Dual Issue GPUs only account for a small portion of the PC gaming market. With RDNA 5, support will span Xbox, PlayStation, and PC. That’s a much more attractive proposition.
What remains to be seen is if AMD’s Dual Issue support with RDNA 5 is strong enough to deliver more seamless utilisation. After all, AMD’s theoretical performance gains are far from a reality. Will Dual Issue work as well as expected with RDNA 5? Furthermore, will developers fully embrace this new feature?
This isn’t the only thing that will improve with RDNA 5
With RDNA 5, AMD has already promised a suite of hardware improvements. Alongside Sony, AMD has unveiled several new features that will debut with its next-generation graphics cards. For boosted AI performance, AMD has Neural Arrays. For boosted ray tracing performance, AMD has Radiance Cores. To boost memory performance and efficiency, there is also “Universal Compression”. More information about these features is available here.
You can join the discussion on AMD’s RDNA 5 graphics improvements on the OC3D Forums.
