netdev - Peak TCP performance

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Message-ID: <CAJoZ4U2eVUd4JiGQ6UFYMdoEwyN=MO8+9S3jGcsaYGN2vqt=3g@mail.gmail.com>
Date:	Thu, 10 Oct 2013 22:34:22 -0400
From:	Kyle Hubert <khubert@...il.com>
To:	netdev@...r.kernel.org
Subject: Peak TCP performance

I'm working on a device, I consistently get 27gbps via netperf-2.6.
UDP reports 54gbps.

TCP is maxed out at 100% CPU on the transmit side. On the receive
side, 40% of the CPU. Thus, I didn't believe I could eek anymore
performance out of it.

However, very oddly, if I enabled bridged mode to forward some
packets, TCP performance goes up to 32gbps. The thing that bothers me
is that transmit CPU utilization drops to 65%, and receive CPU
utilization increases to 60%.

What happens when the device becomes bridged to gain so much
performance? Also, can I now take advantage of the extra CPU time
available to drive more traffic? No tunable seems to have any effect..
(except down)

Any ideas?

Cheers,
-Kyle
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