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Move away from BBR as congestion control algorithm #359

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zorun opened this issue Jan 31, 2020 · 2 comments
Closed

Move away from BBR as congestion control algorithm #359

zorun opened this issue Jan 31, 2020 · 2 comments

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@zorun
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@zorun zorun commented Jan 31, 2020

All servers were switched to the BBR congestion control algorithm:
openstreetmap/chef@67c05c6
https://lists.openstreetmap.org/pipermail/dev/2020-January/030873.html

For tiles, it was not an issue because files are very small. But for larger downloads, BBR is known to behave very unfairly. In particular, in some circumstances, it can generate massive amount of packet loss and completely crush non-BBR streams.

Quoting from this paper:

On the one hand, the intended behavior
of BBR could be observed with our experiments. On the other
hand, some severe inherent issues such as increased queuing
delays, unfairness, and massive packet loss were also detected.

Thus, I would suggest to revert this change. At the very least, this would likely improve the situation for the 1 Gbit/s uplink mentioned in the mailing list discussion above: currently, anybody that can pull files at more than ~600 Mbit/s may cause massive packet loss for all streams.

@pnorman

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@pnorman pnorman commented Feb 23, 2020

We're back on cubic: openstreetmap/chef@484bf30

@pnorman pnorman closed this Feb 23, 2020
@Firefishy

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@Firefishy Firefishy commented Feb 23, 2020

@zorun Appreciated the heads up. We'll wait for BBR v2. If you spot anything else, we'd be happy to hear from you.

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