[Planetlab-users] concerning the behavior of planetlab2.cs.virginia.edu in the last two weeks

[Manfred Georg]

I know I didn't read the previous message :P (though I'm not running anything
anywhere currently)

Manfred

On Wed, 16 Aug 2006, Jeff Hoye wrote:

> Livia,
>
> We are running an ePost node on that computer, but I don't suspect it is a 
> major consumer of CPU.
>
>  However, may I suggest that execution time is not a good measurement of 
> your application performance in PlanetLab?  If you look at a typical 
> planetlab load average (using top) you will find that it is usually above 10 
> (I've seen it as high as 60 sometimes).  Interestingly (and obviously) these 
> load averages go up dramatically before a major conference deadline.  There 
> are probably a lot of applications running on any particular node, and we are 
> all competing for CPU.  I would imagine that there are also all sorts of 
> periodic tasks in experiments that will cause the load to fluctuate 
> dramatically.  Because of all of this, I'm concerned that you will have way 
> too much noise in your experiments if you use execution time as the metric. 
> Perhaps someone can suggest a system tool that will tell you how much CPU 
> your program has used so that you can get a better idea of this metric.  As 
> far as I know there is no system in PlanetLab to schedule CPU time on 
> particular nodes, though there is a signup for bandwidth.
>
> Also, I know that not everyone using planetlab reads every message on this 
> list.  So you probably aren't going to get a complete answer as to who is 
> running applications on a particular node.  Though I recall seeing a status 
> page somewhere that says who is the primary user of any particular resource 
> on a per-node basis.
>
> All, let me know if I am incorrect on any of this.
>
> Thanks!
> -Jeff
>
>
> Livia Maria Rodrigues Sampaio wrote:
>> Hello all,
>> 
>> I have been running some experiments using a distributed application 
>> (implemented by myself) in the planet-lab with 5 nodes, including 
>> planetlab2.cs.virginia.edu. In the last two weeks the performance of my 
>> application slowed down. As such performance depends on the workload of the 
>> node planetlab2.cs.virginia.edu I suppose this node slowed down due to some 
>> reason. I would like to have more information about such workload 
>> variability because this is very important to my performance studies. 
>> Particularly, If you have also been using this node in your experiments you 
>> can contribute with my studies.  The objective of my experiments is to 
>> analyze the performance of a distributed
>> application using the execution time as performance metric.
>> In one of the experiments I used
>> messages of 32KB. The execution time of the application was around 1 
>> second.
>> However, from july 29th to august 13th, such execution times increased to
>> 180 seconds. Presently, august 16th, the execution times are again around
>> 1 second. The variability in the performance of the application is 
>> associated with the workload of the node  planetlab2.cs.virginia.edu. It 
>> seems that the node was "fast" and became "slow" for some
>> period. This is not surprising in the planet-lab as pointed out in the 
>> paper "Fixing the embarrassing slowness of OpenDHT on Planetlab". However, 
>> I would like to have more information about the slowness of this specific 
>> node.
>> In order to put some light on this topic I started investigating two 
>> possibilities: variabilities in the network load (to/from the
>> node) or in the processing load (in the node). In the first
>> case, I collected some
>> traceroute data, in the periods the node was "fast" and "slow", trying to 
>> find some
>> communication bottleneck - in this case, I configured the traceroute to 
>> send messages of 1KB. The traceroute data described the transmission of a 
>> message from each of the 5 nodes considered in my experiments to the same 
>> destination. I didn't noticed anything strange in the logs. Consequently, I 
>> suppose the reason for the variability in the performance of my application 
>> was due to an intensive use of the resources (eg. CPU, memory) of 
>> planetlab2.cs.virginia.edu by a number of applications running on this 
>> node, during the observed period, concurrently with my own application. 
>> Particularly, memory bound application can cause more swapout of the files 
>> been used. Moreover, applications with high priority can use more cpu 
>> cycles than the others.
>> 
>> Another possibility is the intensive use of bandwidth causing fairsharing 
>> of available bandwidth, in this case, each slice of the same node cannot 
>> use the bandwidth limit specified for it. I suppose this is more critical 
>> as the number of applications running in different slices but on the same 
>> node increases.
>> 
>> I would appreciate a lot if you could help me on this topic in the 
>> following way:
>> 
>> 1. Have anybody run applications on planetlab2.cs.virginia.edu during the 
>> period from july 29th to august 13th? Is your application memory bound or 
>> does it require high bandwidth?
>> 2. Is it possible to get information about CPU usage or memory consumption 
>> of a planet-lab node during some period in the past in order to identity 
>> the behavior of the applications competing with my own for the resources in 
>> the node planetlab2.cs.virginia.edu?
>> 
>> I am looking forward to hearing from you...
>> Lívia
>> 
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