Eisenmonoxid1 opens a discussion on how to programmatically distinguish between physical and logical processor cores in cross-platform .NET apps, sharing technical constraints and potential approaches.

Detecting Physical vs Logical Processors in Cross-Platform .NET Applications

Author: Eisenmonoxid1

Problem Statement

In building a cross-platform .NET 9 application, the goal is to:

  • Retrieve the number of available processors
  • Determine for each whether it is a physical core or a logical (HT/SMT) processor
  • Build a processor bitmask based on this information

Current Challenges

  • .NET exposes Environment.ProcessorCount, which gives only the logical processor count.
  • There appears to be no cross-platform mechanism within .NET to distinguish between physical and logical processors directly.

Platform-Specific Approaches

Windows

  • Windows Management Instrumentation (WMI) or P/Invoke (Platform Invocation) can be used to extract detailed processor information on Windows platforms.

Linux/macOS

  • On Linux, /proc/cpuinfo presents detailed information about CPU cores and threads, though parsing is required. For the macOS platform, equivalent facilities may exist but are not addressed in detail here.

Linux Example Command

cat /proc/cpuinfo

Cross-Platform Strategy

  • No .NET-native, uniform API exists for all operating systems.
  • The proposed approach is to detect the operating system at runtime and call the relevant native API or parse system files as appropriate.
  • Microsoft documentation (see referenced doc) provides guidance on guarding platform-specific API usage:

Processor Architecture Clarifications

  • All logical processors are ultimately backed by one or more physical cores.
  • Not all physical cores use Hyper-Threading (HT) or Simultaneous MultiThreading (SMT).
  • Solely knowing the number of logical processors (e.g., 32) does not suffice to infer the number of physical processors, due to possible architectural variations (e.g., 16 dual-threaded cores vs. 32 single-threaded cores).

Example

  • The Intel i9-14900K has 32 logical processors and 24 physical cores. The breakdown can vary between architectures and manufacturers, highlighting the difficulty of a universal software solution.

Key Takeaways

  • Platform-specific code or scripting is required to identify physical vs. logical processors cross-platform.
  • .NET developers should combine environment detection with system file parsing or native API calls.
  • The hardware landscape and OS reporting may introduce ambiguity that cannot always be resolved in a fully generic fashion.

References:

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