The Zen 5 “Granite Ridge” client CPUs, featuring two CCDs with up to 8 working cores each, have been experiencing issues with inter-CCD latency. Reports indicate that the Ryzen 9 9950X has a CCD-to-CCD latency of around 180 ns, which is more than double the latency found in the Ryzen 9 7950X. Fortunately, AMD is reportedly working on a fix for this issue.
Earlier this month, it was suggested that AMD might have rushed the release of the Zen 5 Ryzen 9000 CPUs before the accompanying software was fully developed. Consequently, the Zen 5 CPUs showed marginal performance improvements over their Zen 4 predecessors. The performance issues have been partly attributed to a faulty Core Parking feature on multi-CCD chips like the Ryzen 9 9900X and Ryzen 9 9950X.
An analysis found that the inter-CCD latency in the Ryzen 9 9950X is around 180 ns, compared to just 76 ns in the Ryzen 9 7950X. This discrepancy is believed to stem from buggy software, given that both the Ryzen 9 9950X and the Zen 4 chips use the same I/O die and Infinity Fabric. Additionally, even with Linux in high-performance mode, the Ryzen 9 9950X did not achieve latency levels similar to the Ryzen 9 7950X, indicating that the issue is not limited to Windows.
AMD is reportedly planning to address this latency issue through a BIOS update rather than new hardware changes. This suggests that the Ryzen 9000 series may have been released before the software was fully optimized. While there is no specified timeline for when this BIOS update will be available, addressing the CCD latency issue is expected to result in significant performance improvements for Zen 5 CPUs. Stay tuned for updates on this development.
