[tor-dev] Is Arti expected to have better multi-CPU support than C-tor?

[David Fifield]

Linus Nordberg and I are preparing a submission for FOCI about the
special way we run tor on the Snowflake bridge. We run many tor
processes with the same identity and onion keys, because otherwise tor
being limited to one CPU would be the main bottleneck.

I'm writing to fact-check a claim about Arti and how we hope the current
complicated procedure will not be needed in the future:

	The first and most important bottleneck to overcome is the
	single-threaded nature of the Tor implementation.² A single Tor
	process is limited to one CPU core: once Tor hits 100% CPU, the
	performance of the bridge is capped, no matter the speed of the
	network connection or the number of CPU cores

	²We expect that Arti, the in-progress reimplementation of Tor,
	will be natively multi-threaded, and remove this primary
	complication.

Is this correct? Is a relay that uses a future version of Arti expected
to be able to use all its CPU resources?

Here is the a draft of the submission. If you have any comments, our
submission deadline is 2023-03-15.

https://www.bamsoftware.com/papers/pt-bridge-hiperf/pt-bridge-hiperf.20230307.pdf
https://www.bamsoftware.com/papers/pt-bridge-hiperf/pt-bridge-hiperf.20230307.tex