Quoting Iain Learmonth (2020-01-20 16:00:01)
Last time I looked you could not switch TCP congestion control algorithm in Linux per-namespace (maybe you can now and you don't need to have multiple VMs).
It's been allowed for about two years now [0], but you don't need it anyways. Trying out new congestion control algorithms is not exactly a new fad, so it has been possible to set the congestion control algorithm via setsockopt since, apparently, Linux 2.6.13 [1], released a good 15 years ago. You'd probably need to patch tor to do that effectively, but if you're going to all this trouble anyways, patching one program shouldn't really be a barrier.
[0] https://github.com/torvalds/linux/commit/6670e152447732ba90626f36dfc015a13fb... [1] http://man7.org/linux/man-pages/man7/tcp.7.html