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Date: Wed, 25 Mar 2015 15:01:57 +0000
From: Bruce Richardson <bruce.richardson@intel.com>
To: Cheng Kevin <k5896246@gmail.com>
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Cc: dev@dpdk.org
Subject: Re: [dpdk-dev] DPDK testpmd, Virtual Disk IO limitation
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On Wed, Mar 25, 2015 at 10:06:48PM +0800, Cheng Kevin wrote:
> Hi all,
> 
>    I am a beginner of DPDK. Recently, i am interest in DPDK vHost app -
> testpmd.
> 
>    And i have been tracing on testpmd.c and iofwd.c for a while.
> 
>    Also add some code inside iofwd.c for storing the payload of packets.
> 
>    Everything goes fine, and the performance is great as expected.
> 
>    But when i use fwrite to store the payload into a file,
> 
>    the performance decrease from 800mbps to 3mbps (input stream is 1 Gbps).
> 
>    Is is caused by the limitation of Virtual Disk IO? How can i solve it?
> 
>    I have tried to search the answer, some people say "pthread" might solve
> the problem.
> 
>    Can someone give me some hint, i really appreciate for your help.
> 
> 
> Best Regard,
> 
> Kevin Cheng

Two general issues you will hit writing to disk:
1) IO, including disk IO, is slow
2) System calls are slow.

You are probably hitting both bottlenecks.

/Bruce