dtl_ring
struct dtl_ring *dtlr = &per_cpu(dtl_rings, dtl->cpu);
static DEFINE_PER_CPU(struct dtl_ring, dtl_rings);
struct dtl_ring *dtlr = this_cpu_ptr(&dtl_rings);
struct dtl_ring *dtlr = &per_cpu(dtl_rings, dtl->cpu);