Question

Is there an equivalent api like getloadavg() that can be used within the kernel i.e. for my own driver ?

I have a driver that is thrashing and I would like to throttle it, and i am looking for a kernel-api to find about the cpu usage.

Thank you.

Answer 1

You’re probably looking for the get_avenrun() function in kernel/sched.c. An example of how to use it is in fs/proc/loadavg.c:

static int loadavg_proc_show(struct seq_file *m, void *v)
{
        unsigned long avnrun[3];

        get_avenrun(avnrun, FIXED_1/200, 0); 

        seq_printf(m, "%lu.%02lu %lu.%02lu %lu.%02lu %ld/%d %d\n",
                LOAD_INT(avnrun[0]), LOAD_FRAC(avnrun[0]),
                LOAD_INT(avnrun[1]), LOAD_FRAC(avnrun[1]),
                LOAD_INT(avnrun[2]), LOAD_FRAC(avnrun[2]),
                nr_running(), nr_threads,
                task_active_pid_ns(current)->last_pid);
        return 0;
}

Though I’m a little skeptical of how you can use the load average to modify a driver — the load average is best treated as a heuristic for system administrators to gauge how their system changes over time, not necessarily how “healthy” it might be at any given moment — what specifically in the driver is causing troubles? There’s probably a better mechanism to make it play nicely with the rest of the system.