Ryzen 9000 Zen 5 Inter-Core Latency Bug Fixed With This New AMD Firmware

AMD's desktop Ryzen processors with more than 8 cores are fabricated using chiplets: one big die handles memory, I/O, and other functions, while smaller dice called "CCDs" contain the Zen CPU cores. This approach has a ton of advantages, but a few downsides too, and one of the latter is that core-to-core latency for communications across disparate CCDs is significantly higher than on a monolithic CPU.

This is a well-known and understood phenomenon, but hardware enthusiasts were surprised to learn that AMD's new many-core Zen 5 processors, the Ryzen 9 9900X and Ryzen 9 9950X, had nearly triple the inter-core latency of its previous-generation Zen 4 processors. Some folks even went as far as to blame the somewhat lackluster performance uplift of Ryzen 9000 (over Ryzen 7000) on this quirk.

Well, as it happens, AMD has figured out the cause of this curiosity and completely resolved it in a microcode update. The first BIOS updates are rolling out with AGESA version 1.2.0.2. AGESA stands for "AMD Generic Encapsulated Software Architecture," and AGESA updates actually modify the behavior of the processor at a very low level.

AMD hasn't said a word about it, but independent testing (by domdtxdissar on the Overclock.net forums) of ComboAM5Pi 1.2.0.2 shows radically reduced cross-CCD core-to-core latency—on the order of 2.4x less. Using the CapframeX core-to-core latency tool with an ASUS motherboard and a Ryzen 9 9950X CPU, the Norwegian enthusiast was able to clearly demonstrate the benefits of the new microcode.

So that's great, right? Zen 5's performance woes resolved, and the new AMD CPUs should be much faster now? Well, not exactly. It turns out the practical effect of the high core-to-core latency was really pretty minimal, and while the new microcode definitely helps performance, the actual benefit seems to be pretty small. A user in the thread notes that he "picked up like 1.2K or something points in R23", which sounds very impressive until you realize that a typical Cinebench R23 score for the Ryzen 9 9950X is something like 45,000 points.

Stlil, a 3% performance gain isn't "nothing," and getting a little performance bump out of a free and easy firmware update is absolutely nothing to complain about. We wanted to test the benefits for ourselves, but at the time of this writing, ASRock hasn't pushed AGESA 1.2.0.2 for our X670 Steel Legend motherboard. If you're rocking a Zen 5 CPU, keep an eye on your board's BIOS update page for the new microcode.

^{Thanks to HXL (@9550pro on Xwitter) for the spot.}