Nginx support FTO, however it is disabled in gentoo. FTO is feature supported by multiple packages, another packages are net-dns/nsd, however there is FTO enabled by default, Apache, Unbound. It seems to me, that general USE flag +fto would be useful. Here is guide how to enable FTO on Nginx https://www.unixteacher.org/blog/speed-up-web-delivery-with-nginx-and-tfo/ FTO has to be also enabled in kernel and set properly. As most of android devices come with FTO enabled, nginx and apache could eassily benefit if TFO would be enabled.
its TFO not FTO, sorry for typo
Closing as invalid: There is no real compile option to enable TFO in nginx. Like you can see, configure will check if your system supports TFO (/auto/unix). In this case it will define NGX_HAVE_TCP_FASTOPEN in $S/objs/ngx_auto_config.h. To make use of TFO, you need to enable TFO via sysctl, add fastopen option to nginx.conf and finally you need a client which actually uses TFO (keep in mind that even latest Firefox has TFO disabled by default; and just enabling in client application isn't enough -- you need sysctl option set for outgoing connections, too).
PS: Keep in mind while testing, that you will see TFO only in action with HTTP traffic. But because nowadays most sites are using HTTPS, you won't really see TFO.
*** Bug 694610 has been marked as a duplicate of this bug. ***
