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Date: Tue, 02 Aug 2016 21:24:01 +0200
From: Paul Emmerich <emmericp@net.in.tum.de>
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Subject: [dpdk-users] ixgbe performance on Xeon E3 CPUs with Linux >= 3.16
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Hi,

we've encountered a weird performance issue in a tx only scenario: The 
performance drops by about 30% to 40% with the following configuration.

* i7 or Xeon E3 CPU
* Linux kernel 3.16 or later (tested 3.16, 3.19, and 4.4)
* ixgbe-based NIC

The problem goes away if I either use an Xeon E5, an older Linux kernel 
(tested 3.13 and 3.7), or an i40e-based NIC.

I suspect that this is related to DDIO since a "proper" server CPU 
solves the problem.

Any ideas how to mitigate this? This issue currently keeps us from 
upgrading the OS of an old Ubuntu 14.04.01-based machine.

  Paul