Comment by immibis
2 days ago
Nagle is quite sensible when your application isn't taking any care to create sensibly-sized packets, and isn't so sensitive to latency. It avoids creating stupidly small packets unless your network is fast enough to handle them.
At this point, this is an application level problem and not something the kernel should be silently doing for you IMO. An option for legacy systems or known problematic hosts fine, but off by default and probably not a per SOCKOPT.
Every modern language has buffers in their stdlib. Anyone writing character at a time to the wire lazily or unintentionally should fix their application.
The programs that need it are mostly the ones nobody is maintaining.
TCP_NODELAY can also make fingerprinting easier in various ways which is a reason to make it something you have to ask for.
> The programs that need it are mostly the ones nobody is maintaining
Yes, as I mentioned, it should be kept around for this but off by default. Make it a sysctl param, done.
> TCP_NODELAY can also make fingerprinting easier in various ways which is a reason to make it something you have to ask for
Only because it's on by default for no real reason. I'm saying the default should be off.
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If nobody is maintaining them, do we really need them? In which case, does it really matter?
If we need them, and they’re not being maintained, then maybe that’s the kind of “scream test” wake up we need for them to either be properly deprecated, or updated.
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I think you’re forgetting how terminals work.
So to be clear, you believe every program that outputs a bulk stream to stdout should be written to check if stdout is a socket and enable Nagle's algorithm if so? That's not just busywork - it's also an abstraction violation. By explicitly turning off Nagle's, you specify that you understand TCP performance and don't need the abstraction, and this is a reasonable way to do things. Imagine if the kernel pinned threads to cores by default and you had to ask to unpin them...
No, the program should take care to enable TCP_NODELAY when creating the socket. If the program gets passed a FD from outside it's on the outside program to ensure this. If somehow the program very often gets outside FDs from an oblivious source that could be a TCP socket, then it might indeed have to manually check if it really wants Nagle's algorithm.
> That's not just busywork - it's also an abstraction violation.
You used AI to write this didn't you? Your sentence structure is not just tedious - it's a dead give-away.
If by "latency" you mean a hundred milliseconds or so, that's one thing, but I've seen Nagle delay packets by several seconds. Which is just goofy, and should never have been enabled by default, given the lack of an explicit flush function.
A smarter implementation would have been to call it TCP_MAX_DELAY_MS, and have it take an integer value with a well-documented (and reasonably low) default.
It delays one RTT, so if you have seen seconds of delays that means your TCP ACK packages were received seconds later for whatever reason (high load?). Decreasing latency in that situation would WORSEN the situation.
Maybe, maybe not, whatever.
I was testing some low-bandwidth voice chat code using two unloaded PCs sitting on the same desk. I nearly jumped out of my skin when "HELLO, HELLO?" came through a few seconds late, at high volume, after I had already concluded it wasn't working. After ruling out latency on the audio side, TCP_NODELAY solved the problem.
All respect to Animats, but whoever thought this should be the default behavior of TCP/IP had rocks in their head, and/or were solving a problem that had a better solution that they just didn't think of at the time.
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Reminds me of trying to do IoT stuff in hospitals before IoT was a thing.
Send exactly one 205 byte packet. How do you really know? I can see it go out on a scope. And the other end receives a packet with bytes 0-56. Then another packet with bytes 142-204. Finally a packet a 200ms later with bytes 57-141.
FfffFFFFffff You!
If you were using TCP, then this is absolutely normal and expected behavior. It is a stream protocol, not packet/message based.
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Things like these make me cry
If only there was some sort of User Datagram Protocol where you could send specifically tuned packets like this.
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