netdev - Re: Receive offloads, small RCVBUF and zero TCP window

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Date:   Mon, 28 Nov 2016 16:14:04 -0500
From:   Alex Sidorenko <alexandre.sidorenko@....com>
To:     David Miller <davem@...emloft.net>
Cc:     netdev@...r.kernel.org
Subject: Re: Receive offloads, small RCVBUF and zero TCP window

On Monday, November 28, 2016 3:54:59 PM EST David Miller wrote:
> From: Alex Sidorenko <alexandre.sidorenko@....com>
> Date: Mon, 28 Nov 2016 15:49:26 -0500
> 
> > Now the question is whether is is OK to have icsk->icsk_ack.rcv_mss
> > larger than MTU.
> 
> It absolutely is not OK.
> 
> If VMWare wants to receive large frames for batching purposes it must
> use GRO or similar to achieve that, not just send vanilla frames into
> the stack which are larger than the device MTU.
> 

As VMWare's vmxnet3 driver is open-sourced and part of generic kernel, do you think the problem is in that driver or elsewhere? I looked at vmxnet3 sources and see that it uses LRO/GRO subroutines. Unfortunately, I don't understand its logic enough to see whether they are doing anything incorrectly.

Alex 

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Alex Sidorenko	email: asid@....com
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