rcu-0.2: cbits/pause_impl.h

// adapted from ghc/includes/stg/SMP.h

static __inline__ void _pause(void)
{
#if defined(i386_HOST_ARCH) || defined(x86_64_HOST_ARCH)
    // On Intel, the busy-wait-nop instruction is called "pause",
    // which is actually represented as a nop with the rep prefix.
    // On processors before the P4 this behaves as a nop; on P4 and
    // later it might do something clever like yield to another
    // hyperthread.  In any case, Intel recommends putting one
    // of these in a spin lock loop.
    __asm__ __volatile__ ("rep; nop");
#else
    // nothing
#endif
}