AMD’s Phoenix 2 Hybrid “big.LITTLE” CPU Tested

AMD has been reluctant to adopt a hybrid core architecture, making all its mainstream offerings a homogeneous Zen 4 design with a shared L3. Regardless, there are certain heterogeneous designs that split the workloads between Zen 4 and Zen 4c cores. The Ryzen “Phoenix 2” processor powering the ASUS ROG Ally and a bunch of other handhelds is one such example. Courtesy of David Huang, we get to look at the individual performance characteristics.

At stock, the Zen 4 “P” core is roughly 30% faster than the Zen 4 Dense “E” core in the SPEC CPU 2017 Integer benchmark. Making the clock speeds static at 3.2GHz on both cores results in a tie, verifying that they are based on the same microarchitecture.

In Cinebench R23 (multi-threaded), the 25W Ryzen 7 7840U (Zen 4 x8) is nearly 20% faster than the 30W Z1 hybrid core processor. Remember that the latter also features faster LPDDR5X-7500 memory while the former is paired with LPDDR5-6400.

The voltage/frequency graph indicates that the Zen 4 Dense cores are more efficient between 500MHz to 1,500MHz, after which the Zen 4 core takes the lead in performance and power efficiency.

The SPECint2017 Energy Efficiency test was done using SKUs paired with different memory kits and hence can’t be used for an apples-to-apples comparison. Regardless, the Phoenix 2 chip offers higher performance from 7W to 15W. This could also be due to or in part due to the LPDDR5X memory (versus LPDDR5 on the 7840U), but we can’t say anything for sure.

These tests show that AMD’s Phoenix 2 hybrid CPU offers superior power efficiency than existing Zen 4 designs without changing the ISA. At the same time, many of the advantages of the Zen 4 Dense cores are limited to low-frequency workloads, which get eradicated in high-performance workloads. We’ll just have to wait for a next-gen heterogeneous Ryzen CPU to better understand how Team Red is handling this particular challenge.

Areej Syed

Processors, PC gaming, and the past. I have written about computer hardware for over seven years with over 5000 published articles. I started during engineering college and haven't stopped since. On the side, I play RPGs like Baldur's Gate, Dragon Age, Mass Effect, Divinity, and Fallout. Contact: areejs12@hardwaretimes.com.
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