** Changed in: linux-aws (Ubuntu Groovy)
Status: Fix Committed => Fix Released
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https://bugs.launchpad.net/bugs/1910200
Title:
aws: network performance regression due to initial TCP receive buffer
size change
Status in linux-aws package in Ubuntu:
New
Status in linux-aws source package in Bionic:
Fix Released
Status in linux-aws source package in Focal:
Fix Released
Status in linux-aws source package in Groovy:
Fix Released
Bug description:
[Impact]
AWS has seen some customers reporting networking performance
degradation after they upgraded their Ubuntu instanceses. This
regression is highly impacting customers who are using MTU=9000 (which
is the default in EC2).
[Test case]
Bug reproduced internally in AWS (no test case provided), but
apparently it is very easy to reproduce simply by measuring networking
performance.
[Fix]
AWS worked internally and found that the regression has been
introduced by:
a337531b942b ("tcp: up initial rmem to 128KB and SYN rwin to around
64KB")
To solve the problem we need to apply the following upstream commit
that explicitly fixes the problem introduced by the commit above:
33ae7b5bb841 ("tcp: select sane initial rcvq_space.space for big
MSS")
[Regression potential]
Upstream fix that is only affecting the initial TCP buffer space and
allows the TCP window size to be dynamically increased, basically
restoring the previous (correct) behavior, so regression potential is
minimal.
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