Geoff Chappell, Software Analyst
The KAFFINITY_EX structure is used by the kernel to represent an arbitrary boolean property per processor. It is essentially a dressing-up of a bitmap that allows one bit per processor. Outside the kernel, the structure is opaque. The kernel exports functions that support a range of operations such as setting, clearing and counting bits. All date from version 6.1 unless otherwise noted:
The KAFFINITY_EX structure is not documented. Neither are the functions, though they are declared in the NTOSP.H from the Enterprise edition of the Windows Driver Kit (WDK) for Windows 10 Version 1511.
The KAFFINITY_EX expands as successive Windows versions allow more processor groups:
|Version||Size (x86)||Size (x64)|
|6.2 to 10.0||0x0C||0xA8|
Sizes, offsets, types and names in the table that follows are from Microsoft’s symbol files for the kernel.
KAFFINITY Bitmap [MAX_PROC_GROUPS];
Here, a macro, MAX_PROC_GROUPS, is presumed for the maximum number of processor groups:
The Count and Size count processor groups. They are initially 1 and MAX_PROC_GROUPS. The Count grows, up to the Size, as bits get set further into the bitmap.