linux-kernel - Re: Got iperf regression while intel_iommu is on, how to cut the cost of cache flushing

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Date:	Thu, 31 Oct 2013 08:25:36 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Ethan Zhao <ethan.kernel@...il.com>
Cc:	Ashok Raj <ashok.raj@...el.com>, Shaohua Li <shaohua.li@...el.com>,
	Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
	Fenghua Yu <fenghua.yu@...el.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Got iperf regression while intel_iommu is on, how to cut the
 cost of cache flushing

On Thu, 2013-10-31 at 10:44 +0800, Ethan Zhao wrote:
> Hi guys,
> 
>      We got network I/O performance degradation with latest stable
> kernel and the be2net driver as compared to old kernel 3.0.6.   later
> we found even compared to
> the same latest stable kernel but the INTEL_IOMMU set to 'n',  still
> got very noticeable performance regression:
> 
> Kernel   : 3.11.x with  CONFIG_INTEL_IOMMU_DEFAULT_ON not set
> Network driver    : be2net
> 
> Average Bandwidth for :
>    1.tcp-unidirectional test    : 7908 Mbits/sec
>    2.tcp-unidirectional-parallel: 9400 Mbits/sec
>    3.tcp-bidirectonal test      : 5464 Mbits/sec
> 
> Kernel   : 3.11.x with CONFIG_INTEL_IOMMU_DEFAULT_ON set
> Network driver    : be2net

You might hit a known problem for some 10Gb links.

3.12-rc6 has the fixes already, and stable has some pending backports :

commit 95bd09eb27507691520d39ee1044d6ad831c1168
tcp: TSO packets automatic sizing

commit c9eeec26e32e087359160406f96e0949b3cc6f10
tcp: TSQ can use a dynamic limit

Please check that current 3.12-rc6 is OK ?



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