netdev - Re: [net PATCH] i40e/i40evf: Limit TSO to 7 descriptors for payload instead of 8 per packet

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Date:	Wed, 30 Mar 2016 13:15:04 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Sowmini Varadhan <sowmini.varadhan@...cle.com>
Cc:	Jesse Brandeburg <jesse.brandeburg@...el.com>,
	Alexander Duyck <alexander.duyck@...il.com>,
	Alexander Duyck <aduyck@...antis.com>,
	Netdev <netdev@...r.kernel.org>,
	intel-wired-lan <intel-wired-lan@...ts.osuosl.org>,
	Jeff Kirsher <jeffrey.t.kirsher@...el.com>
Subject: Re: [net PATCH] i40e/i40evf: Limit TSO to 7 descriptors for payload
 instead of 8 per packet

On Wed, 2016-03-30 at 16:09 -0400, Sowmini Varadhan wrote:
> On (03/30/16 12:41), Jesse Brandeburg wrote:
> > This gets "Even Uglier", I've turned off all offloads at my receiver,
> > enabled calling skb_linearize on *all* frames, which works fine for
> > scp, but the receiver shows > MSS sized frames on the wire for
> > rds-stress traffic.
> 
> fwiw, I was not able to reproduce this tx issue with iperf/netperf
> etc either (I tried various perumtations of bidir, req-resp etc). One
> difference between the rds-stress invocation and the other callers
> is that this comes down via tcp_sendpage(), I dont know if there
> is something in the sendpage path that i40e does not anticipate. 

You might try netperf -t TCP_SENDFILE -- -m 150

to let netperf use sendfile() on small frags.