Hi,

> There is an alternate algorithm for pthread_once that doesn't require
> a barrier in the common case, which I've considered implementing. But
> it does need efficient access to thread-local storage. At one time,
> this was a kinda bad assumption (especially legacy mips is horribly
> slow at TLS) but nowadays it's probably the right choice to make, and
> we should check that out again...

1¡¢Can we move dmb after we get the value of control£¿ like this£º

int __pthread_once(pthread_once_t *control, void (*init)(void))
{
    /* Return immediately if init finished before, but ensure that
    * effects of the init routine are visible to the caller. */
    if (*(volatile int *)control == 2) {
        // a_barrier();
        return 0;
    }

    a_barrier();
    return __pthread_once_full(control, init);
}

2¡¢Can we use 'ldar' to  instead of dmb here? I see musl
already use 'stlxr' in a_sc.  like this:

static inline int load(volatile int *p)
{
	int v;
	__asm__ __volatile__ ("ldar %w0,%1" : "=r"(v) : "Q"(*p));
	return v;
}

if (load((volatile int *)control) == 2) {
    return 0;
}

...


Chuang Yin