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

The window length of the windowed min filter to track the minimum RTT. A shorter window lets a flow more quickly pick up new (higher) minimum RTT when it is moved to a longer path (e.g., due to traffic engineering). A longer window makes the filter more resistant to RTT inflations such as transient congestion. The unit is seconds. Default: 300