code: func (s *RegionRequestSender) SendReq(bo *Backoffer, req *tikvrpc.Request, regionID RegionVerID, timeout time.Duration) (*tikvrpc.Response, error) {
  	resp, _, err := s.SendReqCtx(bo, req, regionID, timeout)
  	return resp, err
  }
docs: // SendReq sends a request to tikv server.