[tor-relays] Bridge with iat-mode=2 very slow

[David Fifield]

On Tue, Sep 26, 2023 at 02:22:06PM +0000, Split via tor-relays wrote:
> I run the obfs4 bridge, in the parameters I specify to use iat-modr=2. As a
> result, the bridge is VERY, VERY SLOW. Connection speed is on average 100 kb/
> sec. When I remove the iat-mode=2 parameter, the speed becomes 8-10 times
> higher.
> 
> I checked the processor load, it is at 3%, the problem is unlikely to be with
> the processor, the RAM load is at 20%. I can't figure out if this is expected
> behavior or if the speed drop is too significant. Please tell me, is this the
> normal maximum speed of the bridge with iat-mode=2 or can it be increased
> somehow?

I don't know what's a typical bandwidth range to expect, but it's
expected that iat-mode=2 is much slower than normal. Use iat-mode=1 for
less aggressive traffic shaping.

Some old visualizations of iat-mode's effect on packet sizes and timing:
https://www.bamsoftware.com/talks/pets-2017-menace/#figures