FreeBSD 12.0, ядро GENERIC

После включения
net.inet.tcp.fastopen.server_enable=1

и добавления в nginx:
fastopen=512 reuseport

через пару часов TTFB веб-сервера увеличилось на 50% с 40ms до 60ms.

Никаких ошибок и предупреждений в dmesg, messages и логах nginx нет.

# netstat -m
1068/5907/6975 mbufs in use (current/cache/total)
1025/2767/3792/507450 mbuf clusters in use (current/cache/total/max)
1/2276 mbuf+clusters out of packet secondary zone in use (current/cache)
4/152/156/253724 4k (page size) jumbo clusters in use (current/cache/total/max)
0/0/0/75177 9k jumbo clusters in use (current/cache/total/max)
0/0/0/42287 16k jumbo clusters in use (current/cache/total/max)
2333K/7618K/9951K bytes allocated to network (current/cache/total)
0/0/0 requests for mbufs denied (mbufs/clusters/mbuf+clusters)
0/0/0 requests for mbufs delayed (mbufs/clusters/mbuf+clusters)
0/0/0 requests for jumbo clusters delayed (4k/9k/16k)
0/0/0 requests for jumbo clusters denied (4k/9k/16k)
342594 sendfile syscalls
339831 sendfile syscalls completed without I/O request
4844 requests for I/O initiated by sendfile
24783 pages read by sendfile as part of a request
2955606 pages were valid at time of a sendfile request
0 pages were valid and substituted to bogus page
0 pages were requested for read ahead by applications
0 pages were read ahead by sendfile
0 times sendfile encountered an already busy page
0 requests for sfbufs denied
0 requests for sfbufs delayed

Ошибок на сетевых интерфейсах нет:
# netstat -I em0 -w1
            input            em0           output
   packets  errs idrops      bytes    packets  errs      bytes colls
       545     0     0      38223         19     0       7943     0
       525     0     0      37749         40     0      33904     0
       584     0     0      39423         47     0      36448     0
       498     0     0      32155         16     0       1206     0
       505     0     0      35556         23     0       7342     0
       449     0     0      31518         77     0      91866     0
       410     0     0      29821         44     0      40494     0
       521     0     0      36320         48     0      43210     0
       629     0     0      64184        181     0     218778     0
       540     0     0      37414         43     0      29004     0
       646     0     0      49110        178     0     216789     0
       483     0     0      35183          9     0       2704     0
       496     0     0      34001         22     0       3708     0
       546     0     0      43146         74     0      56049     0
       680     0     0      55448         19     0       4499     0
       517     0     0      39827         87     0      93620     0
       480     0     0      33521         27     0      27582     0
       357     0     0      25930         12     0        840     0
       352     0     0      40406          5     0        414     0
       510     0     0      36331         46     0      38386     0
       503     0     0      35555         39     0      32041     0