When AMD came back nine years ago with the Zen core, its strategy was to eliminate the split between big and little (Bobcat and Jaguar) cores and cover the entire market with a single, balanced architecture. Intel, on the other hand, moved to hybrid (big.LITTLE) CPUs. AMD is apparently going there too, now. It has used classic and compact cores where both shared the same architecture so far, but now there will be a separate low-power core.
This low-power core is expected to serve the same role as Intel’s so-called LP E-Cores, whose purpose is not to increase multi-threaded performance, but to efficiently handle background tasks and other lightweight workloads, instead. This is particularly beneficial for laptops. During idle or light workloads, the system can run exclusively on a few LP E-Cores while most of the processor remains powered down, leaving only a low-power “island” with the LP E-Cores active. When used properly, LP E-Cores can therefore improve laptop battery life, although in theory they could also be used in desktop PCs to reduce power consumption outside of heavy workloads.
AMD has now officially confirmed that its upcoming processors will feature a new core type designated “Low Power”—this appeared in code submitted to Linux that adds support for these cores. According to AMD engineers, this is a third core type alongside the existing “Performance” and “Efficiency” cores (referring to the standard big/classic Zen 4 and Zen 5 cores and the compact “dense” Zen 4c and Zen 5c cores).
These cores will have dedicated identifiers so that the operating system, as well as user applications, can detect them as Low Power cores (the same infrastructure already distinguishes between Performance and Efficiency cores) and take this into account when assigning workloads to individual cores.
The submitted patch does not explicitly state that this technology will debut in AMD’s upcoming Zen 6 processors, but that is highly likely. Leaks presented by YouTuber Moore’s Law Is Dead had already suggested the integration of LP cores, and these claims are now partially confirmed. LP cores will almost certainly appear in Ryzen “Medusa” laptop processors (Medusa Point and other variants), which are expected to launch in 2027 (hopefully in the first half of the year).
It is less certain whether desktop Zen 6 processors for the AM6 socket (codenamed Olympic Ridge) will also include LP cores. They could certainly reduce idle power consumption, but we expect AMD to omit them from desktop processors to save die area—and therefore reduce the cost—of the I/O chiplet. There are also rumors that these processors may even lack integrated graphics, although those reports have not been fully confirmed. It is possible they simply mean that most desktop CPUs will have the iGPU disabled, even though the silicon physically contains it, with some models still shipping with graphics enabled. But the chances of LP cores appearing in desktop Olympic Ridge processors are probably lower than the chances that they will retain the integrated graphics.
A hybrid of Zen 6 and Zen 5?
Intel uses the same “Atom” core architecture (currently, for example, Skymont and Darkmont) for LP E-Cores as it does for its standard E-Cores. The difference is that LP E-Cores operate at lower clock speeds and are not connected to the ring bus and L3 cache, further reducing their performance. According to reports circulating online, AMD may take a different approach. The LP cores in Ryzen processors are apparently being developed as a separate architectural branch and will differ from both the standard Zen 6 cores and the compact Zen 6c cores.
However, this architecture may not be a completely independent evolutionary branch unrelated to the mainstream cores. According to rumors (whose origin is not very clear, though), AMD will likely base this low-power core on an architecture evolved from Zen 5, albeit possibly with various simplifications. What we are currently referring to as Zen 6 LP (whether that will be the official name remains unknown) could therefore also be described as Zen 5 LP. Earlier leaks did, in fact, claim that Zen 6 processors would be paired with Zen 5 LP cores, which may actually be explained by Zen 6 LP actually being close to Zen 5. Perhaps older AMD documents tended to designate the core based on that.
To allow this core to operate seamlessly alongside Zen 6 cores, however, AMD will incorporate all changes affecting the instruction set and software compatibility. From the software’s perspective, Zen 6 LP will therefore present itself as a Zen 6 generation core, even though internally it will function more like Zen 5 and will likely offer substantially lower performance than Zen 6.
Ryzen processors—at least those intended for laptops—will therefore lose some of their previous homogeneity. Although the instruction set will remain compatible across all threads, CPUs will now contain three different core types: full-fledged Zen 6 cores with high single-threaded performance; compact Zen 6c cores offering the same architecture and IPC (performance per MHz), but with a significantly lower maximum clock speed; and finally Zen 6 LP cores. These will not only operate at lower clock speeds, but will also deliver lower performance per 1 MHz. In addition, some instructions (for example, AVX-512 shuffle operations sound like possible candidates) may suffer substantially reduced performance beyond that—their implementation may be only rudimentary, intended to ensure correct compatibility rather than respectable execution speed. It is also possible, for example, that the LP cores will not support SMT. However, since LP cores are not intended to boost high-performance multi-threaded workloads, this should not be a significant drawback.
Source: Phoronix
English translation and edit by Jozef Dudáš
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