netdev - Re: TSQ accounting skb->truesize degrades throughput for large packets

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Date:	Fri, 6 Sep 2013 17:36:42 +0100
From:	Zoltan Kiss <zoltan.kiss@...rix.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	Wei Liu <wei.liu2@...rix.com>,
	Jonathan Davies <Jonathan.Davies@...citrix.com>,
	Ian Campbell <ian.campbell@...rix.com>,
	<netdev@...r.kernel.org>, <xen-devel@...ts.xenproject.org>
Subject: Re: TSQ accounting skb->truesize degrades throughput for large packets

On 06/09/13 13:57, Eric Dumazet wrote:
> Well, I have no problem to get line rate on 20Gb with a single flow, so
> other drivers have no problem.
I've made some tests on bare metal:
Dell PE R815, Intel 82599EB 10Gb, 3.11-rc4 32 bit kernel with 3.17.3 
ixgbe (TSO, GSO on), iperf 2.0.5
Transmitting packets toward the remote end (so running iperf -c on this 
host) can make 8.3 Gbps with the default 128k tcp_limit_output_bytes. 
When I increased this to 131.506 (128k + 434 bytes) suddenly it jumped 
to 9.4 Gbps. Iperf CPU usage also jumped a few percent from ~36 to ~40% 
(softint percentage in top also increased from ~3 to ~5%)
So I guess it would be good to revisit the default value of this 
setting. What hw you used Eric for your 20Gb results?

Regards,

Zoli
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