throtl_peek_queued
while ((bio = throtl_peek_queued(&sq->queued[READ])) &&
while ((bio = throtl_peek_queued(&sq->queued[WRITE])) &&
bio != throtl_peek_queued(&tg->service_queue.queued[rw]));
bio == throtl_peek_queued(&sq->queued[rw]))
bio = throtl_peek_queued(&sq->queued[READ]);
bio = throtl_peek_queued(&sq->queued[WRITE]);