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by marginalia_nu 1374 days ago
On the one hand, sure, you can probably squeeze some cycle or two out of buffering everything in memory. Even though your disk read is a memory read in all likelihood given how filesystem caching works, it's still an IO call, which isn't free.

Keeping everything in user space buffers might just be faster.

On the other hand, you're sending that sucker over network, and what you save doing this is most likely best counted in microseconds/request. It's piss in the ocean compared to the delay introduced even over a local network.
1 comments
tsimionescu 1374 days ago
> Even though your disk read is a memory read in all likelihood given how filesystem caching works, it's still an IO call, which isn't free.

I wonder if io_uring could be used to issue a single syscall that would read data from disk (actually using page cache) and send it on the network.

Of course, you could use DPDK or similar technologies to do the opposite - read the data from disk once and keep it in user-space buffers, then write it directly to NIC memory without another syscall. That should still theoretically be faster, since there would be 0 syscalls per request, where the other approach would require 1 per request.

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Matthias247 1374 days ago
> I wonder if io_uring could be used to issue a single syscall that would read data from disk (actually using page cache) and send it on the network.

Only if you don't care about HTTP/2 and TLS. And if you don't care about those, you can as well do sendfile() from a thread.

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toast0 1374 days ago
You can do kernel TLS for sendfile at least, maybe for io_uring too? Probably not for HTTP/2, but I'm not convinced multiplexed tcp in tcp is a good protocol for the public internet anyway.
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Matthias247 1374 days ago
That's indeed possible, if one has a TLS stack which supports KTLS. I however don't think there's not too many of those yet, and probably even less so in Rust where both the library and a potential Rust wrapper would need to support it.
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xena 1374 days ago
My site does serve itself out of a UNIX socket, so sendfile() may actually work. But most of the data is served with handler functions though.
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