Zhaoxin, a joint venture between Via Technologies and the Shanghai Municipal Government, is adding support for 'preferred cores' in their processors into the Linux kernel, mirroring the approach that Intel and AMD have used for years. The move is designed to improve the single-thread performance of Zhaoxin's CPUs by distinguishing cores that can reach higher frequencies than others, thus pinning latency-sensitive work into the fastest cores.
General-purpose cores in multi-core processors tend to have different clock rate potentials: some of them can achieve higher operational frequencies, leading to a disparity among the cores and the necessity to bind certain workloads to these cores to get higher overall performance. This is why Zhaoxin has introduced a series of patches to the Linux kernel, as reported by Phoronix.
These patches enable the Linux kernel's scheduler to recognize and prioritize tasks on these high-performing cores by using the ACPI CPUFreq driver that relies on the cppc_get_highest_perf function in the CPPC driver. Once the driver detects the frequency of each core, it recognizes the highest frequency value as a priority indicator for the scheduler to set core priorities and favor these preferred cores.
However, there is a catch about these Zhaoxin patches: they lack specific details about the CPUs they are meant to support. Whether this preferred cores feature is currently available in Zhaoxin processors or is intended for future CPUs, such as the upcoming Kaixian KX-7000 based on the Century Avenue architecture, remains unclear.
Meanwhile, Phoronix notes that Zhaoxin has recently put a lot of effort into patching the Linux kernel for its Yongfeng (CentaurHauls) microarchitecture, which powers the KaiSheng KH-40000 processors that are aimed primarily at data centers.
Assigning certain workloads to preferred cores makes a lot of sense for data center and consumer applications, so adding support for this feature to Linux is good news for those who plan to use Zhaoxin CPUs. It also emphasizes that Zhaoxin is gaining functionality akin to CPUs from AMD and Intel.
