netdev - Re: is non-inheritance of congestion control algorithm from the listen socket a bug or a feature?

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Message-Id: <20111129.165205.91103035999089185.davem@davemloft.net>
Date:	Tue, 29 Nov 2011 16:52:05 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	ycheng@...gle.com, rick.jones2@...com, netdev@...r.kernel.org
Subject: Re: is non-inheritance of congestion control algorithm from the
 listen socket a bug or a feature?

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Tue, 29 Nov 2011 22:46:15 +0100

> Le mardi 29 novembre 2011 à 13:20 -0800, Yuchung Cheng a écrit :
>> I actually think it's a feature :)
>> 
>> I find it awkward to set CC on listening socket. And current document
>> defines the sysctl well
>> 
>> tcp_congestion_control - STRING
>>         Set the congestion control algorithm to be used for new
>>         connections. The algorithm "reno" is always available, but
>>         additional choices may be available based on kernel configuration.
>>         Default is set as part of kernel configuration.
> 
> This might be a feature, but contradicts most socket options set on
> listener and inherited by a child socket on accept()

There is really no reason to keep the current behavior.

If an application sets the congestion control algorithm on a listening
socket to a non-default value, what effect could possibly be intended?

Congestion control doesn't even come into play at all on a listening
socket, therefore the only logical expectation is that it inherits to
the child.

The only other logical behavior would be to forbid this operation on a
listening socket, since it has no effect, but that doesn't make any
sense now does it? :-)
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