"Operation not permitted" while creating RT thread with "pthread_create"

[foool]

hardware: 3C5000
kernel: 6.7
glibc: 2.38
gcc: 13.2.1

Encountering errors when trying to create threads using pthread_create. While creating regular threads poses no issues, attempting to modify their scheduling policy to FIFO and adjust priorities results in errors. Specifically, pthread_create returns 1. Uncertain whether this is due to a system limitation or not.

here is the code:

#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <sched.h>
#include <errno.h>
#include <string.h>


void *thread_function(void *arg) {

    printf("Hi\n");

    return NULL;
}


int main() {
    pthread_t my_thread;
    int ret;
    struct sched_param param;
    pthread_attr_t attr;

    ret = pthread_attr_init(&attr);
    if (ret != 0) {
        perror("pthread_attr_init");
        exit(EXIT_FAILURE);
    }

    ret = pthread_attr_setschedpolicy(&attr, SCHED_FIFO);
    if (ret != 0) {
        perror("pthread_attr_setschedpolicy");
        exit(EXIT_FAILURE);
    }

    ret = pthread_attr_getschedparam(&attr, &param);
    if (ret != 0) {
        perror("pthread_attr_getschedparam");
        exit(EXIT_FAILURE);
    }

    param.sched_priority = sched_get_priority_max(SCHED_FIFO);
    ret = pthread_attr_setschedparam(&attr, &param);
    if (ret != 0) {
        perror("pthread_attr_setschedparam");
        exit(EXIT_FAILURE);
    }

    ret = pthread_attr_setinheritsched(&attr, PTHREAD_EXPLICIT_SCHED);
    if (ret != 0) {
        perror("pthread_attr_setinheritsched");
        exit(EXIT_FAILURE);
    }

    ret = pthread_create(&my_thread, &attr, thread_function, NULL);
    if (ret != 0) {
        perror("pthread_create");
        fprintf(stderr, "pthread_create failed: %s, (%d)\n", strerror(ret), ret);
        exit(EXIT_FAILURE);
    }

    ret = pthread_join(my_thread, NULL);
    if (ret != 0) {
        perror("pthread_join");
        exit(EXIT_FAILURE);
    }

    printf("Thread joined\n");

    pthread_attr_destroy(&attr);

    return 0;
}

[yetist]

我试了在 x86 archlinux 上运行时结果相同。

如果去掉 pthread_attr_setinheritsched 函数调用部分，则能正常运行。

应该是设置了调度策略，内核会做优先级检查，无法通过检查。

[foool]

谢谢您的回复，看来这是一般情况，和架构无关。
扩展到一般情况，创建非0 优先级任务的都有类似问题，感觉很可能是内核升级后的一个特性。
用strace 发现，是sched_scheduler 系统调用返回了错误：

clone3({flags=CLONE_VM|CLONE_FS|CLONE_FILES|CLONE_SIGHAND|CLONE_THREAD|CLONE_SYSVSEM|CLONE_SETTLS|CLONE_PARENT_SETTID|CLONE_CHILD_CLEARTID, child_tid=0x7ffff0d5f270, parent_tid=0x7ffff0d5f270, exit_signal=0, stack=0x7ffff055c000, stack_size=0x802a60, tls=0x7ffff0d5f900} => {parent_tid=[5013]}, 88) = 5013
sched_setscheduler(5013, SCHED_FIFO, [99]) = -1 EPERM (Operation not permitted)

看到这个回答 https://unix.stackexchange.com/a/511261/141940 我意识到可能和rt throttling 有关，于是关闭之

sudo bash -c "echo -1 > /proc/sys/kernel/sched_rt_runtime_us"

问题就消失了，sched_setscheduler 也返回正常了

clone3({flags=CLONE_VM|CLONE_FS|CLONE_FILES|CLONE_SIGHAND|CLONE_THREAD|CLONE_SYSVSEM|CLONE_SETTLS|CLONE_PARENT_SETTID|CLONE_CHILD_CLEARTID, child_tid=0x7ffff17c7270, parent_tid=0x7ffff17c7270, exit_signal=0, stack=0x7ffff0fc4000, stack_size=0x802a60, tls=0x7ffff17c7900} => {parent_tid=[5026]}, 88) = 5026
sched_setscheduler(5026, SCHED_FIFO, [99]) = 0

我暂时也没找到内核哪里对这个有描述，或者这么做的合理性。