ACK: [SRU][B/aws, F/aws, G/aws][PATCH 0/1] aws: fix network performance regression due to initial TCP buffer size change

[William Breathitt Gray]

On Tue, Jan 05, 2021 at 08:44:41AM +0100, Andrea Righi wrote:
> BugLink: https://bugs.launchpad.net/bugs/1910200
> 
> [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 this regression has been introduced
> by:
> 
>  a337531b942b ("tcp: up initial rmem to 128KB and SYN rwin to around 64KB")
> 
> To solve this 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.

Acked-by: William Breathitt Gray <william.gray at canonical.com>
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