CODEWITHSUNDEEP
linuxmultithreadingprocess
merlin2011
merlin2011

Reputation: 75555

How can I unpin a thread after pinning to a core using sched_setaffinity?

I am currently using sched_setaffinity to pin a thread to a particular CPU core.

void setCpuAffinity(int id) {                                            
    cpu_set_t cpuset;                                                    

    CPU_ZERO(&cpuset);                                                   
        CPU_SET(id, &cpuset);                                            
        assert(sched_setaffinity(0, sizeof(cpuset), &cpuset) == 0);      
}

Unfortunately, I cannot find a corresponding function to unpin the thread from any given core, and allow the kernel to schedule the thread on any core.

How can I reverse the effect of CPU pinning and allow free movement of a thread once again?

I am aware that one hack would be to use CPU_OR and add every CPU ID to the allowable set, but I am looking for a less hacky approach that restores the state of a thread to the state before sched_setaffinity was ever called.

Upvotes: 0

Views: 600

Answers (1)

merlin2011
merlin2011

Reputation: 75555

Using @phs's suggestion, I wrote the following two functions, which are called before and after cpu pinning to unpin the thread. This successfully unpins the CPU.

void setCpuAffinity(cpu_set_t cpuset) {                                
    assert(sched_setaffinity(0, sizeof(cpuset), &cpuset) == 0);        
}                                                                      

cpu_set_t getCpuAffinity() {                                             
    cpu_set_t cpuset;                                                    

    CPU_ZERO(&cpuset);                                                   
    assert(sched_getaffinity(0, sizeof(cpuset), &cpuset) == 0);          
    return cpuset;                                                       
}

Upvotes: 1

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