affinity.c

//
// Created by maks on 19.06.2023.
//

#include <linux/limits.h>
#include <stdbool.h>
#include <unistd.h>
#include <stdio.h>
#include <fcntl.h>
#include <stdlib.h>
#include <sched.h>
#include <string.h>
#include <jni.h>

#include "mojoexec.h"

static _Thread_local bool big_core_affine = false;

static cpu_set_t bigcore_affinity_set;
static bool has_affinity_set;

static bool should_use_affinity = false;

#define FREQ_MAX 256
void bigcore_format_cpu_path(char* buffer, unsigned int cpu_core) {
    snprintf(buffer, PATH_MAX, "/sys/devices/system/cpu/cpu%i/cpufreq/cpuinfo_max_freq", cpu_core);
}

static void create_affinity_set() {
    char path_buffer[PATH_MAX];
    char freq_buffer[FREQ_MAX];
    char* discard;
    unsigned long core_freq;
    unsigned long max_freq = 0;
    unsigned int corecnt = 0;
    unsigned int big_core_id = 0;
    while(1) {
        bigcore_format_cpu_path(path_buffer, corecnt);
        int corefreqfd = open(path_buffer, O_RDONLY);
        if(corefreqfd != -1) {
            ssize_t read_count = read(corefreqfd, freq_buffer, FREQ_MAX);
            close(corefreqfd);
            freq_buffer[read_count] = 0;
            core_freq = strtoul(freq_buffer, &discard, 10);
            if(core_freq >= max_freq) {
                max_freq = core_freq;
                big_core_id = corecnt;
            }
        }else{
            break;
        }
        corecnt++;
    }
    printf("MojoExec: big CPU number is %u, frequency %lu Hz\n", big_core_id, max_freq);
    CPU_ZERO(&bigcore_affinity_set);
    CPU_SET_S(big_core_id, CPU_SETSIZE, &bigcore_affinity_set);
    has_affinity_set = true;
}

void mojoexec_make_bigcore_affine() {
    if(big_core_affine) return;
    if(!has_affinity_set) create_affinity_set();
    int result = sched_setaffinity(0, CPU_SETSIZE, &bigcore_affinity_set);
    if(result != 0) {
        printf("MojoExec: setting affinity failed: %s\n", strerror(result));
    }else{
        printf("MojoExec: forced current thread onto big core\n");
        big_core_affine = true;
    }
}

JNIEXPORT void JNICALL
Java_git_artdeell_mojoexec_MojoExec_setUseBigCoreAffinity(JNIEnv *env, jclass clazz, jboolean enable) {
    should_use_affinity = enable;
}