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

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Date:	Tue, 12 Nov 2013 09:03:14 +0800
From:	Ethan Zhao <ethan.kernel@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Ashok Raj <ashok.raj@...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

Eric,
    We have tested the performance with the TSO and TSQ patches
merged, the result not good, even worse than kernel without those two
patches. any idea ?

kernel   : 3.11.x with TSO & TSQ merged.  ( CONFIG_INTEL_IOMMU_DEFAULT_ON=y )
Network Interface : eth4
Network driver    : be2net

Average Bandwidth for :
   1.tcp-unidirectional test    : 4385 Mbits/sec
   2.tcp-unidirectional-parallel: 9383 Mbits/sec
   3.tcp-bidirectonal test      : 2755 Mbits/sec

vs

kernel   :  3.11.x without TSO & TSQ patches.
(CONFIG_INTEL_IOMMU_DEFAULT_ON is not set)
Network Interface : eth4
Network driver    : be2net

Average Bandwidth for :
   1.tcp-unidirectional test    : 7992 Mbits/sec
   2.tcp-unidirectional-parallel: 9403 Mbits/sec
   3.tcp-bidirectonal test      : 5802 Mbits/sec

Thanks,
Ethan

On Thu, Oct 31, 2013 at 11:25 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> 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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