file: /proc/sys/net/ipv4/tcp_thin_linear_timeouts
variable: net.ipv4.tcp_thin_linear_timeouts
Official reference

Enable dynamic triggering of linear timeouts for thin streams. If set, a check is performed upon retransmission by timeout to determine if the stream is thin (less than 4 packets in flight). As long as the stream is found to be thin, up to 6 linear timeouts may be performed before exponential backoff mode is initiated. This improves retransmission latency for non-aggressive thin streams, often found to be time-dependent. For more information on thin streams, see Documentation/networking/tcp-thin.txt Default: 0