关于i7-8750H的Runtime调用返回值及并行线程数的技术咨询

Hey there, let's tackle your two questions about the i7-8750H and Java parallel computing in plain terms:

1. Will Runtime.getRuntime().availableProcessors() return 6 or 12? #

This method returns the number of logical processors the JVM can access. The i7-8750H has 6 physical cores, and with Hyper-Threading (enabled by default on almost all systems), each physical core shows up as 2 logical threads to the operating system.

Under normal desktop conditions (no CPU restrictions from virtualization, power management, or system settings), this method will return 12. The only time you'd get 6 is if Hyper-Threading is disabled in your BIOS/UEFI, or if the system is limiting the CPU to just physical cores.

2. Is 12-thread parallelism better than 6-thread for simple parallel tasks? #

It depends on what your "simple" tasks are doing—here's the breakdown:

• Pure CPU-bound tasks (raw number crunching): If your work is just basic math loops or computations with no waiting for memory or IO, Hyper-Threading won't give you a big lift. The two logical threads per core share the same physical resources, so running 6 threads (one per physical core) might be more efficient—you avoid resource contention between the logical threads on the same core, leading to smoother, more consistent performance.
• Tasks with minor waiting/light memory operations: Even simple tasks can have brief pauses (like waiting for data to load from memory into the CPU cache). In these cases, 12 threads help keep the physical cores busy: while one logical thread is waiting, the other can use the core's resources to make progress. This can lead to small but noticeable speedups.
• Super fine-grained tasks: If your parallel work is split into tiny chunks, the overhead of managing 12 threads (context switching, scheduling) could cancel out any gains. For really small tasks, sticking to 6 threads minimizes this overhead and might be faster.

If you can, test both setups with your actual workload! For most simple parallel tasks, 12 threads will either match or slightly outperform 6, but pure CPU-heavy simple tasks might see marginal gains or even a tiny dip with 12 threads.

内容的提问来源于stack exchange，提问作者gscp