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Date: Wed, 25 Mar 2015 17:32:48 +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 Thu, Mar 26, 2015 at 12:20:42AM +0800, Cheng Kevin wrote:
> Mr. Bruce Richardson
> 
> Yes, you are right. This really bother me.
> 
> Is there any way to get rid of system call? Maybe some DPDK threading API?
> Maybe i should use a extra nic card for posting the data out through
> internet, instead of writing on the disk - ex. fwrite.
> 
> Or you have some better advises??
> 
> Thanks
> Kevin
> 

Hi Kevin,

what is your end-goal that you are trying to get to? 

/Bruce

> 
> 2015-03-25 23:01 GMT+08:00 Bruce Richardson <bruce.richardson@intel.com>:
> 
> > 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
> >