DOS ain't dead

Detection on processor cores and hyperthreading (Announce)

posted by Laaca , Czech republic, 25.01.2021, 15:35

> What method described on OSdev you use? In my CPUID I use CPUID way, too
> scared to mess with ACPI ;) I'll post results later.

I use the ACPI scan. You have to parse RSDP -> RSDT -> MADT and parse the processor-ACPI records.
It detects all logical cores and it is not so difficult.

The problem is to distinquish whether the reported core is physical core or virtual core from hyperthreading.

The proper approach is to take the ACPI-ID from each reported core (byte value) and parse individual bits. Because 7-2 bits (or 7-1 bits) identifies the physical core and low 0 bit (or 0-1 bits) identifies the hyperthreaded core.

To get the information whether the right division for physical/hyperthreaded bits is 5-3 or 6-2 or 7-1 you should use the CPUID instruction.

I do not use the CPUID but rely on the recomended (or mandatory?) order how the cores should be reported from ACPI.

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DOS-u-akbar!

Complete thread:

• Detection on processor cores and hyperthreading - Laaca, 25.01.2021, 00:28 (Announce)
  • Detection on processor cores and hyperthreading - roytam, 25.01.2021, 06:51
  • Detection on processor cores and hyperthreading - RayeR, 25.01.2021, 13:55
    • Detection on processor cores and hyperthreading - Laaca, 25.01.2021, 15:35
      • Detection on processor cores and hyperthreading - RayeR, 25.01.2021, 17:08
        • Detection on processor cores and hyperthreading - RayeR, 25.01.2021, 17:09
          • Detection on processor cores and hyperthreading - Laaca, 25.01.2021, 18:36
            • Detection on processor cores and hyperthreading - RayeR, 26.01.2021, 03:00