[Enhancement] UDP sockets improve with sendmmsg/recvmmsg

[zonyitoo]

• Linux: https://man7.org/linux/man-pages/man2/sendmmsg.2.html
• FreeBSD: https://www.freebsd.org/cgi/man.cgi?query=send&sektion=2
• macOS: https://github.com/apple/darwin-xnu/blob/main/bsd/sys/socket.h#L1433
• Windows: https://docs.microsoft.com/en-us/windows/win32/api/mswsock/nc-mswsock-lpfn_transmitpackets

Speedtest: shadowsocks/shadowsocks-org#194 (comment)

Batch send and recv UDP packets will significantly increase the upper limit of speed for UDP channels.

Works have to be done:

• Find a proper way (zero-cost abstraction) for sendmmsg and recvmmsg on these 4 platforms
• Making UDP association channels to be compatible with batch send / recv
• Proper way to fallback (when sendmmsg/recvmmsg are not supported)

If anyone interested to make it available, PRs are welcome.

[dev4u]

遇到未知情况：是否因为没有区分bypass流量，还是proxy流量，在微信语音通话时，通话质量不好。
表现为：在对方说话过程中，己方想插一句话，对方没办法听到。就像无线对讲机的那种体验。

[zonyitoo]

sendmmsg and recvmmsg are not used in actual code yet.

[dev4u]

sendmmsg and recvmmsg are not used in actual code yet.

那可能是我的ipv6问题，回去我确认一下。

[dev4u]

那可能是我的ipv6问题，回去我确认一下。

万恶的，几天前开始就把我出国的ipv6流量全掐断了。

多包合发、多包合收的功能什么时候可以开放呢？ipv4的使用体验不是太好，想看看这个能不能提升使用质量。

[zonyitoo]

Do not expect sendmmsg/recvmmsg can improve user experience in poor network environment. sendmmsg/recvmmsg is just for reducing syscalls, which will eventually increase the upper limit of performance.

[database64128]

The GFW enforces much fewer rules on IPv6. I think you should do a traceroute to make sure it's not your local network's problem.

[dev4u]

其实对于移动手机用户来说，体验好并不等于上网速度快。更多追求的是电池续航更长点、网络请求响应迅速点。
或许这也是大佬们说的，别压榨尽手机的极限能力吧。
sendmm、recvmm，正是把多次包合并一次来处理。在理论上，应该能延长电池续航能力。

[dev4u]

The GFW enforces much fewer rules on IPv6. I think you should do a traceroute to make sure it's not your local network's problem.

先放几天再试，毕竟最近网上太多事情发生了，有可能受不知哪个事件的影响导致的。

[database64128]

Turns out FreeBSD's sendmmsg(2) is just a compatibility shim in its libc. It still makes sendmsg(2) syscalls. https://github.com/freebsd/freebsd-src/blob/main/lib/libc/gen/sendmmsg.c

Therefore it should be removed from the list.