Affinity mask
An affinity mask is a bit mask indicating what processor(s) a thread or process should be run on by the scheduler of an operating system.[1] Setting the affinity mask for certain processes running under Windows can be useful as there are several system processes (especially on domain controllers) that are restricted to the first CPU / Core. So, excluding the first CPU might lead to better application performance.
Windows API
Thread affinity in Microsoft Windows can be specified with the SetThreadAffinityMask
function.[1] Forcing of each OpenMP thread to distinctive cores in Windows can be accomplished by means of the following C code:
#include <windows.h>
#include <omp.h>
// Set OpenMP thread affinity
void set_thread_affinity () {
#pragma omp parallel default(shared)
{
DWORD_PTR mask = (DWORD_PTR )1 << omp_get_thread_num();
SetThreadAffinityMask(GetCurrentThread(), mask);
}
}
See also
References
- "SetThreadAffinityMask function (winbase.h) - Win32 apps". learn.microsoft.com. January 27, 2022. Retrieved April 7, 2023.
External links
- MSDN article on SetThreadAffinityMask function
- Taskset, a tool to set the affinity mask on Linux
- CPU Balancer, a free, open-source utility that distributes Windows XP processes uniformly over logical processors using the affinity mask
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