netdev - Re: data vs overhead bytes, netperf aggregate RR and retransmissions

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Date:	Wed, 3 Aug 2011 23:37:32 -0700
From:	Jesse Brandeburg <jesse.brandeburg@...il.com>
To:	Rick Jones <rick.jones2@...com>
Cc:	netdev@...r.kernel.org
Subject: Re: data vs overhead bytes, netperf aggregate RR and retransmissions

On Tue, Aug 2, 2011 at 2:39 PM, Rick Jones <rick.jones2@...com> wrote:
> driver: igb
> version: 2.1.0-k2
> firmware-version: 1.8-2
> bus-info: 0000:05:00.0
>
> One of the things fixed recently in netperf (top-of-trunk, beyond 2.5.0) is
> I actually have reporting of per-connection TCP retransmissions working.  I
> was looking at that, and noticed a bunch of retransmissions at the 256 burst
> level with 24 concurrent netperfs.  I figured it was simple overload of say
> the switch or the one port active on the SUT (I do have one system talking
> to two, so perhaps some incast).  Burst 64 had retrans as well.  Burst 16
> and below did not.  That pattern repeated at 12 concurrent netperfs, and 8,
> and 4 and 2 and even 1 - yes, a single netperf aggregate TCP_RR test with a
> burst of 64 was reporting TCP retransmissions.  No incasting issues there.
>  The network was otherwise clean.

Rick, can you reboot and try with idle=poll OR set ethtool -C ethX rx-usecs 0
both tests would be interesting, possibly relating your issue to cpu
power management and/or interrupt throttling, or some combo of both.

Also please check the ethtool -S ethX stats from the hardware, and
include them in your reply.
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