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

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Message-ID: <20160330204023.GK27540@oracle.com>
Date:	Wed, 30 Mar 2016 16:40:23 -0400
From:	Sowmini Varadhan <sowmini.varadhan@...cle.com>
To:	Eric Dumazet <eric.dumazet@...il.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 (03/30/16 13:15), Eric Dumazet wrote:
> You might try netperf -t TCP_SENDFILE -- -m 150
> 
> to let netperf use sendfile() on small frags.

that still did not reproduce it but let me try beating on
that approach with more permutations.

BTW, another data-point that may help debug this: even with i40e,
if you use the "-o" option to the rds-stress invocation, there are
no problems: the "-o" option  enforces uni-directional data
transfer, so one side is pure-Tx, other side is pure-Rx. 

It is only when both sides simultaneously do both Tx and Rx
on the tcp socket that you see the issue. I dont know if
that provides any clues.

--Sowmini