SMP and Network Connections

Douglas Eadline deadline at plogic.com
Thu Apr 17 14:04:03 EDT 2003


On Thu, 17 Apr 2003, Joseph Mack wrote:

> Douglas Eadline wrote:
> > 
> > Just posted some more SMP tests on www.cluster-rant.com.
> > This time, I tested the interconnects and asked the
> > question "What if a dual SMP used two Ethernet connections
> > instead of one?" Seems to help! Take a look at:
> 
> Thanks for your work and write up. 
> 
> I did some performance tests a few years ago on a router,
> using multiple copies of netpipe through a single interface 
> to a set of nodes, to determine the effect of multiple streams
> on throughput on the router (this was 100Mbps ethernet).
> 
> I found that as I increased the number of nodes connecting
> to the router, that the throughput increased, rising above
> 100Mbps (when I totalled the throughput from each netpipe
> job).
> 
> Looking at the netpipe code I saw that netpipe waits for a
> quiet time on the network before entering the next round of
> the test. Thus for 4 connections, if each instance of
> netpipe waited for a quiet time to run the test on the next
> packet size, I could (in principle) get the result of 4 connections
> of 100Mpbs for a total of 400Mpbs. 
> 
> I contacted the netpipe author, who sent me a preliminary version
> of a multi-netpipe, where multiple connections are synchronised
> and stepped through the range of packet sizes together. He
> said that it wasn't ready to use and I didn't have time to 
> work on it myself. I never solved the multiple connection 
> problem and wound up doing tests with a single connection.
> 
> Do you know if this problem is affecting your measurements?

I was not aware of this, however, the netpipe data seems to 
indicate that when two netpipes are using the same interface,
there is some degradation when compared to a single run. I'll have a look 
at the code as well. Thanks for the information. 

Doug




> 
> (The report is at
> http://www.linuxvirtualserver.org/Joseph.Mack/performance/single_realserver_performance.html)
> 
> Joe
> 
> 

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