How to Set CPU Affinity of a Process

How to Set CPU Affinity of a Process

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

Web Server

Ngix

With Ngix 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:```php system(‘taskset -cp 0,1 ‘.getmypid());


### C++ code

On Linux, please refer to the following code snippet:```cpp
#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:```cpp #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```shell
$ taskset –p 22445
pid 22445’s current affinity list: 0-5

Set a process’s CPU affinity to 0-2 CPUs```shell $ 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```shell
$ 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. task-manager-affinity Then, click “Set affinity”. processor-affinity Method 3: Start /affinity Launch a command window and run the highlighted commands as follows Run```shell cd C:\Windows\system32\inetsrv\

Run```shell
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 IDAssociated value (n)Formula (2n-1)Affinity in Hex (h)
CPU0111
CPU1233
CPU2477
CPU3815F
CPU416311F
CPU532633F
CPU6641277F
CPU7128255FF

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.```shell 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.```shell
Start /affinity 11 BarcodeReaderDemo.exe

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

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