Mapping logical processors to physical processors

Question

On a dual quad-core GetProcessAffinityMask (or the dialog from "Set affinity" in taskman.exe) will report eight logical processors. How do I find out which logical processor is on which physical processor? Especially: which logical processors are on the same physical processor?

EDIT: If it is not possible to do this programmatically, do anyone just know what the normal mapping is? Are the first four on the first processor and the second four on the second or are the odd numbered on the first and the even numbered on the second?

Answer 1

You can use Win32_Processor WMI class to query the number of cores, number of logical processors, architecture, cache memory and other information about the CPUs on the system.

To query information about the relationship between the logical processors in a system, you can use GetLogicalProcessorInformation API function.

Answer 2

In case you don't want to write the code yourself, SysInternal's handy coreinfo utility comes closest to answering your questions. It implements GetLogicalProcessorInformation as Mehrdad recommends. For a Xeon E5640 (quad core, 8 threads), you get from coreinfo:

c:\App\SysInternals>Coreinfo.exe -c

Coreinfo v3.0 - Dump information on system CPU and memory topology
Copyright (C) 2008-2011 Mark Russinovich
Sysinternals - www.sysinternals.com

Logical to Physical Processor Map:
**------  Physical Processor 0 (Hyperthreaded)
--**----  Physical Processor 1 (Hyperthreaded)
----**--  Physical Processor 2 (Hyperthreaded)
------**  Physical Processor 3 (Hyperthreaded)

There are 8 * for the 8 hyperthreads, two per core, as expected for this chip. What's not clear, though, is how the arrangement of * matches up with the list of logical processors as Windows presents them. For instance, Task Manager gives me a dialog for assigning the processor affinity, labeled CPU 0 through CPU 7, for any process. It's fair (but not necessary) to assume that you can take coreinfo's output and number the logical processors left-to-right. So "CPU 5" would be the second hyperthread running on physical processor 2.

Answer 3

The numbering is done in a sequential manner: first all physical cores followed by the logical cores [1] .

[1] CPU Numbering on a hypertheading enabled system