[uml-devel] UDP vs. TCP performance over UML

[uml-devel] UDP vs. TCP performance over UML

[George Hadjichristofi]

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Dear All,

 

We are doing some UML performance testing and we are getting some
non-sensible UDP statistics.

We have deployed the following network of two nodes:

A--------B

 

Node A is connected to node B via a wired link (100 Mbps) and node A is
running one UML instance. 

We used the Iperf traffic generator to execute performance measurements for
both TCP and UDP.

 

Measurements:

 When we use TCP the throughput is 100 Mbps from the UML instance of node A
to the host kernel of node B and 100 Mbps from the host kernel of node A to
the host kernel of node B.  However, when we use UDP the throughput is only
26 Mbps from the UML instance on node A to the host kernel of node B, but
100 Mbps from the host kernel of node A to the host kernel of node B.  We
also notice that a large number of packets were dropped in the case of UDP
over UML.

 

What is the reason that UDP throughput is so much lower than TCP?

Why are packets being dropped given that Iperf is blocking? 

 

We appreciate any guidance on this matter.

 

Regards,

George Hadjichristofi

WINLAB, Rutgers University

 


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Re: [uml-devel] UDP vs. TCP performance over UML

[Jeff Dike]

On Tue, Jun 12, 2007 at 07:01:05AM -0400, George Hadjichristofi wrote:
>  When we use TCP the throughput is 100 Mbps from the UML instance of node A
> to the host kernel of node B and 100 Mbps from the host kernel of node A to
> the host kernel of node B.  However, when we use UDP the throughput is only
> 26 Mbps from the UML instance on node A to the host kernel of node B, but
> 100 Mbps from the host kernel of node A to the host kernel of node B.  We
> also notice that a large number of packets were dropped in the case of UDP
> over UML.

At what interface are the packets being dropped?

				Jeff

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Re: [uml-devel] UDP vs. TCP performance over UML

[George Hadjichristofi]

Hi Jeff,

We took some more measurements. This is what we have:
A to B with UML: 46Mbps with UDP, 147Mbps with TCP
A to B from Host kernel: 285 Mbps for both UDP and TCP

In the case of A to B (with UML on A) there are packets dropped. Based on
Ifconfig on the host kernel the packets seem to drop between tap0 and eth0
on the host kernel. (i.e., the number of packets on tap0 is higher than
eth0).

Hope that was clear enough. 

Thank you,
George



-----Original Message-----
From: user-mode-linux-devel-bounces@lists.sourceforge.net
[mailto:user-mode-linux-devel-bounces@lists.sourceforge.net] On Behalf Of
Jeff Dike
Sent: Tuesday, June 12, 2007 11:04 AM
To: George Hadjichristofi
Cc: 'shruti singhal'; user-mode-linux-devel@lists.sourceforge.net
Subject: Re: [uml-devel] UDP vs. TCP performance over UML

On Tue, Jun 12, 2007 at 07:01:05AM -0400, George Hadjichristofi wrote:
>  When we use TCP the throughput is 100 Mbps from the UML instance of node
A
> to the host kernel of node B and 100 Mbps from the host kernel of node A
to
> the host kernel of node B.  However, when we use UDP the throughput is
only
> 26 Mbps from the UML instance on node A to the host kernel of node B, but
> 100 Mbps from the host kernel of node A to the host kernel of node B.  We
> also notice that a large number of packets were dropped in the case of UDP
> over UML.

At what interface are the packets being dropped?

				Jeff

-- 
Work email - jdike at linux dot intel dot com

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Re: [uml-devel] UDP vs. TCP performance over UML

[Jeff Dike]

On Tue, Jun 12, 2007 at 08:32:15PM -0400, George Hadjichristofi wrote:
> In the case of A to B (with UML on A) there are packets dropped. Based on
> Ifconfig on the host kernel the packets seem to drop between tap0 and eth0
> on the host kernel. (i.e., the number of packets on tap0 is higher than
> eth0).

ifconfig tells you directly how many packets are dropped.  What does the
"dropped:" field say?

				Jeff

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Work email - jdike at linux dot intel dot com

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