Zen 5 issues: Ryzen 9000 CPUs reportedly suffered development troubles as bugs like flawed core parking surface

When AMD announced the Ryzen 9000 series CPUs at Computex 2024, the company claimed that the new Zen 5 architecture enjoys a 16% average IPC uplift over Zen 4. Team Red also claimed that the Ryzen 9 9950X would be up to 55% ahead of the Core i9-14900K in Blender and up to 23% ahead in titles like Horizon Zero Dawn.

Sadly, the gains, if there are any, appear much more modest in launch reviews of the Zen 5 processors. Naturally, this has made people question AMD’s claims regarding the performance of the Ryzen 9000 CPUs.

So, what’s really going on? Did AMD really lie during its Computex 2024 keynote? Or is the unfinished software holding Zen 5 CPUs back?

To get answers to these questions, serial leaker Tom of the Moore’s Law is Dead (MLID) YouTube channel reached out to his sources from inside AMD and the information, if true, raises some serious questions.

Ryzen 9000 Zen 5 CPUs were reportedly rushed out

One of MLID’s AMD sources claims that Zen 5 was “plagued with problems throughout its development”. The project allegedly moved from team to team, resulting in “many delays and a lot of unnecessary rework”. Zen 5 was seemingly first headed by the Zen 2 team before moving on to other teams within the company.

However, the Zen 2 team reportedly decided to use their own “Zen 2 codebase” and not to build on the one developed by the Zen 4 team. This could have led to unfinished software as the source alleges that AMD likely “rushed the products out the door before the software was finished”.

Additionally, the source also reported to Tom that AMD’s communication to reviewers was lacking as the marketing department “didn’t communicate details about Core Parking to Reviewers until 5 days after they received test samples”.

Core parking is a feature aimed primarily at saving energy by disabling certain cores. When enabled, the feature, at least in theory, boosts gaming performance on Ryzen CPUs with multiple CCDs like the Ryzen 9 9900X and the Ryzen 9 9950X by limiting process threads to one CCD. This reduces performance penalties incurred by cache misses and CCD-to-CCD latency. However, core parking is apparently not working correctly on the Zen 5 CPUs at the time of writing.

Zen 5 software issues

As mentioned by Tom in his video, Zen 5 processors seem to be struggling with core parking issues resulting in performance degradation. According to Anandtech’s analysis, the Ryzen 9 9950X has an inter-CCD latency of 180 ns which is more than twice as much as the 76 ns of the Ryzen 9 7950X (Available on Amazon).

While there is no clear answer as to why there is such a big increase in latency when both the Zen 4 and the Zen 5 share the I/O die and the Infinity Fabric design, Anandtech conjectures that the issue could be the result of faulty core parking where it might be taking 100 ns to reactivate the disabled cores.

Additionally, according to an analysis posted on Level1Linux, the Ryzen 9000 CPUs seem to be performing better in gaming on Linux with a 2-3% increase vs the gains already seen on Windows. There are even some games where, even though the titles are specifically designed for Windows, Zen 5 chips are apparently faster on Linux. So, Windows appears to not be optimized well for Ryzen 9000 processors.

Long story short, it looks like the Ryzen 9000 chips were released before the software was fully ready. It will now be interesting to see what future updates AMD pushes out and how much better the Zen 5 chips get a few months from now.

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