code: func (d *Downloader) requestRTT() time.Duration {
  	return time.Duration(atomic.LoadUint64(&d.rttEstimate)) * 9 / 10
  }
docs: // requestRTT returns the current target round trip time for a download request
  // to complete in.
  //
  // Note, the returned RTT is .9 of the actually estimated RTT. The reason is that
  // the downloader tries to adapt queries to the RTT, so multiple RTT values can
  // be adapted to, but smaller ones are preferred (stabler download stream).