netdev - Re: How to do TCP tx checksums

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Message-ID: <1447784807.22599.125.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Tue, 17 Nov 2015 10:26:47 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Ben Greear <greearb@...delatech.com>
Cc:	Tom Herbert <tom@...bertland.com>, netdev <netdev@...r.kernel.org>
Subject: Re: How to do TCP tx checksums

On Tue, 2015-11-17 at 09:44 -0800, Ben Greear wrote:

> And in case it helps, here is the output from dmesg.
> 
> This is an Ethernet frame, and in this case csum-start is the
> index of the first byte of the TCP header as far as I can tell.
> 
> [64967.194251] check: 0xf51b  csum-start: 34  offset: 16 summed: 0x3  saddr: 0x201010a  daddr: 0x101010a len: 1514
> 

You forgot to clear tcp header @check before calling
__tcp_v4_send_check(), I think.

( th->check = 0; )


Anyway, just use trafgen and get ~6 Mpps, more easily than with pktgen.



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