st_reaped
stp->st_reaped = desc_index;
ASSERT3U(stp->st_reaped, ==, stp->st_completed);
stp->st_reaped = 0;
reaped = stp->st_reaped;
stp->st_reaped = reaped;
level = stp->st_added - stp->st_reaped;
stp->st_reaped, &(stp->st_added))) != 0)
stp->st_completed - stp->st_reaped >= SFXGE_TX_BATCH) {