??????????????
????TCP???1974?????????????????30???????????????????????????Э?顣???????繃???￡?TCP??????絹???????????????????????????????￡????????????в???
???????????????????????????????????????????????????????????4G????????????????????????????????????????????????????????????????????????????????????????????????????????????
???????????????Linux?????????????????????????????????????????????TCP???Щ?????????????????????
????????????????????
????????????????????????????????????Щ????????????TCP Fast Open (TFO)????????????????????????????????????????????????????????????????涼?????У? Linux???3.6??????3.7???????????

?????????????TCP Fast Open: expediting web services
?????????????????
??????ε?HTTP??????ò?????HTML??????????????????????????????(Round-Trip Time)??????????????????????????????м???????????????????????????????????????????????????С????????ó???????????????о???
????3.0?????????????????(initcwnd)??С?3??????????????????????????????3??MSS????1??MSS?1400????????????4K??????????10???????????13K???????
??????辭?????У??????????????WEB?????????initcwnd???ó?10??linux???3.0?汾????????10??????????????????????????á?
???????????????????????????????????????????????????????Щ??
???????????????????????С???????δ???????????4K????????????????????????????????
?????????????
????Tuning initcwnd for optimum performance
????Optimizing Your Linux Stack for Maximum Mobile Web Performance
????An Argument for Increasing TCP's Initial Congestion Window
??????????????????(Head-of-line blocking?? HOL)
????TCPЭ??????????????????????????FIFO?????????У????????????????????????????????????????????????????????????????????????????????????????豸????????ν???????HOL??head-of-line blocking?????????????????????????????????????????Ч??

????1. ??·???ò?????
????HTTP/2????????????·??????????????????????HTTP/1.*??·???????????????????????????TCP???????????????????????TCP???Э????·????????????????????????????С??????·???????????????????
????2. TCP Keepalive?????Ч
??????????TCP??Keepalive???????????????????????????????????????????????????Ч??
??????????NFS?????????????????TCP Keepalive??????????????????????????????????Keepalive??Ч??????????????????????
????3. ?????????????
?????????????????????????????????????????????????????????????????????????????????У??????????????????????????????????????????????Э??????"No route to host"??????????????????16???????????????????????????????????￡???????????????????????????TCPDUMP???????15??????????????"EHOSTUNREACH"??????ò?????????"No route to host"??????
???????壩????????
???????????????????????????????????????ν???????????????????????￡??????Щ????????????????????????????????????????á?