netdev - Re: Re: Re: Re: Re: Re: Re: Re: limited network bandwidth with 3.2.x kernels

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Message-ID: <CADVnQymT6saSSmUmT7BUShfQFoJ+u4JMQ=F2bhRv4vB_Pzj=9Q@mail.gmail.com>
Date:	Wed, 15 Feb 2012 09:49:07 -0500
From:	Neal Cardwell <ncardwell@...gle.com>
To:	alekcejk@...glemail.com
Cc:	Eric Dumazet <eric.dumazet@...il.com>, netdev@...r.kernel.org
Subject: Re: Re: Re: Re: Re: Re: Re: Re: limited network bandwidth with 3.2.x kernels

If there was an increase in the number of bytes charged to the socket
for each skb, without a corresponding increase in TCP receive buffer
size, that would explain a systematic decrease in receiver window that
would cause some paths, like perhaps these, to become
receiver-window-limited (which is consistent with the symptom of
stable bandwidth for a given path).

Can you please try increasing the default TCP receiver window to see
if this helps; try this as root on the 3.2 machine:

sysctl net.ipv4.tcp_rmem="4096 897664 897664"

Basically making the middle number as big as the third number should
bump up the default receiver window size.

neal
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