The Loop Buffer wasn't really doing anything significant to enhance the performance of Ryzen 7000 CPUs and hence, AMD deactivated it.
AMD deactivates Zen 4 Loop Buffer via AGESA 1.2.0.2a patch on AM5 motherboards since Op Cache was sufficient for managing loops
AMD's Loop Buffer technology isn't something you will find on most Ryzen generations. It was only implemented on the Zen 4 architecture CPUs to ensure the front-end pipeline can be bypassed for more optimized performance. Since AMD didn't do it in a well-optimized manner due to the lack of extensive documentation for the developers, it didn't see much benefit from the loop buffer.
The disabling of the loop buffer was first noticed by Chips and Cheese, who came to know about this difference when testing the AMD Ryzen 9 7950X3D on an ASRock B650 PG Lightning motherboard. The loop buffer was fully operational with one of the previous BIOS 1.21, AGESA 1.0.0.6 patch, but stopped functioning with the BIOS 3.10, AGESA 1.2.0.2a patch.
Thankfully, no performance degradation was seen with this update and Zen 4 CPUs can continue working as usual as before. Therefore, the implementation of the loop buffer wasn't deployed in a manner that could really help Zen 4 CPUs to work as expected. Most of the credit goes to the Op Cache, which did the job the loop buffer was meant to do initially.
The loop buffer is basically a small memory storage feature inside Zen 4 CPUs that can hold instructions for loops. These loops are sequences that are repeated several times when a program is executed. With the loop buffer, the process of fetching these instructions from the cache or the memory is canceled/bypassed, which saves power and improves efficiency.
However, the Zen 4 architecture also includes the Op Cache, which is a micro-op cache, which exists in the Zen architectures and has enough bandwidth to store these instructions. This allowed the Zen 4 CPUs to work efficiently even without the Loop Buffer, which was meant to bypass the front-end pipeline. AMD already knew that this wouldn't be a good idea for future Zen architectures and hence, the Zen 5 CPUs don't come with the loop buffer.
Unlike Intel and Arm, which have deployed similar features for their CPUs, AMD wasn't able to optimize the performance with the loop buffer. However, AMD is still good to go with the existing Op Cache mechanism for its Zen CPUs.
News Source: Chips and Cheese
