Why E cores make Apple Silicon fast
Apple Silicon Macs are remarkably fast, and this piece argues that it's not just the powerful P-cores, but the unsung E-cores that make the difference. By offloading background tasks, E-cores ensure that performance cores are always ready for user applications. This technical deep dive into Apple's scheduling and core architecture perfectly captures the type of engineering insight valued by the HN community.
The Lowdown
Many attribute the speed of Apple Silicon Macs to their powerful Performance (P) cores, but the true hero, according to this analysis, is the Efficiency (E) core. These cores are meticulously designed to handle background processes, freeing up P-cores for immediate user tasks and ensuring a consistently smooth and responsive experience.
- When an Apple Silicon Mac starts up, its E-cores are immediately swamped with background tasks like Spotlight indexing, Time Machine backups, and system services, while P-cores remain largely idle.
- This heavy E-core utilization might alarm those familiar with Intel Macs, where similar loads could cripple performance; however, Apple Silicon's architecture is built to manage this without impacting user applications.
- Activity Monitor's 100% E-core utilization display can be misleading, as E-cores operate at much lower frequencies than P-cores.
- The concept of distinguishing between P and E cores, utilizing ARM's big.LITTLE architecture, has been in Apple products since the iPhone 7 and uses a Quality of Service (QoS) system.
- QoS, introduced in OS X 10.10 Yosemite, intelligently allocates threads: foreground tasks prioritize P-cores (but can use E-cores), while background tasks are strictly confined to E-cores.
- This core allocation strategy prevents background processes from monopolizing P-cores, thereby maintaining application responsiveness and optimizing battery life.
- Modern macOS benefits from this by breaking down application tasks into numerous discrete background processes, allowing E-cores to manage a vast number of threads efficiently.
- Newer M-series chips feature an increasing number of E-cores (four to eight, up from two in early M1 Pro/Max models) to further enhance this background processing capability.
Ultimately, E-cores are fundamental to Apple Silicon's performance model, effectively segregating background noise from critical foreground operations, allowing user applications to run without interruption and contributing significantly to the overall snappy feel of these machines.