How to Set CPU Affinity of a Process

Jul 11, 2019

 Business-tips and tricks

There are a few ways to set a process’s CPU affinity. In this article, we will discuss a few options.

Web Server

NGINX

With NGINX on FreeBSD and Linux, you can bind worker processes to a set of CPUs using the worker_cpu_affinity directive. Please find the details here: Worker_cpu_affinity.

IIS

About how to configure CPU usage parameters and CPU actions that will be used in application pools, please refer to CPU Settings for an Application Pool.

Programming

PHP

With PHP, you can set affinity by running taskset program through system() call. For example, below binds the PHP process to cores 0 and 1:

system('taskset -cp 0,1 '.getmypid());

C++ code

On Linux, please refer to the following code snippet:

#define _GNU_SOURCE
#include <sched.h>
#include <stdio.h>
#include <sys/sysinfo.h>

int main()
{
    cpu_set_t  mask;
    CPU_ZERO(&mask);
   
    CPU_SET(0, &mask);
    CPU_SET(1, &mask);
    CPU_SET(2, &mask);
    CPU_SET(3, &mask);
    sched_setaffinity(0, sizeof(mask), &mask);
}

On Windows, please refer to the following code snippet:

#include < Windows.h>

int main()
{
           ::SetProcessAffinityMask(GetCurrentProcess(), 0xf/*first 4 cpus*/);
}

Operating System

Linux

We can run the taskset program to set affinity. Get the CPU affinity of a process

$ taskset –p 22445
pid 22445's current affinity list: 0-5

Set a process’s CPU affinity to 0-2 CPUs

$ taskset –pc  0-2 22445
pid 22445's current affinity list: 0-5
pid 22445's new affinity list: 0-2

Start a process with specified CPU affinity

$ taskset –c 0-3 ./ReadBarcode

Reference: taskset

Windows OS

There are a few different methods to achieve this.

Method 1: System-wide System-wide we can set the boot.ini setting to use /numproc=4 so that the machine only uses 4 cores irrespective of the number of cores available (provided that there are 4 or more cores available)

Method 2: Task Manager First, select a process from Task Manager.

Then, click “Set affinity”.

Method 3: Start /affinity Launch a command window and run the highlighted commands as follows

Run

cd C:\Windows\system32\inetsrv\

Run

start /affinity 1F InetMgr.exe

Now you can check the affinity from the Task Manager or Process Explorer.

If you are using start /affinity, you will need to specify a hexadecimal value for affinity. There is a simple way to calculate affinity value. Here is how the processors will be numbered.

CPU ID	Associated value (n)	Formula (2n-1)	Affinity in Hex (h)
CPU0	1	1	1
CPU1	2	3	3
CPU2	4	7	7
CPU3	8	15	F
CPU4	16	31	1F
CPU5	32	63	3F
CPU6	64	127	7F
CPU7	128	255	FF

Based on the formula above , you can run the following command. Replace h with the value in the Affinity column. This will result in using all the CPUs listed above the specified value including the current. Example: If you specify a value of 1F for affinity, it will use CPU4, CPU3, CPU2, CPU1, and CPU0.

Start /affinity h BarcodeReaderDemo.exe

If you want to use specific CPUs, you will need to SUM the associated values and use the corresponding HEX value. Example: If you want to run a process on CPU0 & CPU4, you can sum the values which is 0x11.

Start /affinity 11 BarcodeReaderDemo.exe

Reference: how-to-launch-a-process-with-cpu-affinity-set

•  CPU-AFFINITY