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Re: Why is my gigabit ethernet so slow?

On Wed, Jan 27, 2010 at 11:06:06AM +0700, Robert Elz wrote:
> Ignoring the TSO problems (which could be almost anything), that result
> and the similar one for the longer test, tell you immediately that the
> "problem" is just the TCP window size.

Yes.  That's why increasing the socket buffer size makes an immediate
difference: in our kernel the maximum window size is constrained by the
socket buffer size.

Why the automatic socket buffer sizing code isn't bringing the socket
buffer size and thus the window size up to 128K by itself over the course
of a 10GB test is not obvious to me.  Either it's buggy, or it isn't
causing the window scaling option to be used (in other words, it's buggy),
I think has to be the answer.


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