[zeromq-dev] Mb vs. MB in tests & on the Wiki

[Martin Hurton]

On Mon, Oct 13, 2008 at 07:17:02PM +0200, Martin Sustrik wrote:
> Hi Holger,
> 
> > I was just having some more fun with the zmq examples when I noticed that
> > all the tests and also the Wiki use [Mb] for throughput. Not to be overly
> > pedantic but unless I'm mistaken that should probably be [MB] since it's
> > megabytes, not -bits. My poor little box is slow but it's certainly better
> > than ~60 MB/sec over loopback. ;)
> 
> It's Mb, not MB. The point is to make it comparable with bandwidth of 
> your network interfaces. For example, if you are running on 1Gb 
> Ethernet, it's useful to know that you are able to exhaust say 534 Mb/s 
> which translates in straightforward way to 53.4%. Reporting it as 66.7 
> MB/s is a little bit less useful.


What about Mbit/s. This would help to avoid the above
mentioned confusion. See http://en.wikipedia.org/wiki/Mbps#Megabit_per_second

> 
> As for performance of your loopback interface, it depends on the message 
> size you are testing. Say you are testing 1 byte long messages. Thus 
> 60MB/s would give 60,000,000 messages a second which is above all limits 
> for today's middleware.
> 
> You should expect your throughput depending on message size to look 
> something like this:
> 
> http://www.zeromq.org/results:0mq-tests-v03#toc4
> 
> For very small messages, CPU power is the bottleneck and thus you won't 
> see your network's bandwidth exhausted (the throughput in 
> messages/second will be more or less stable, while throughput in 
> megabits/second will be quite small, but growing). At the point where 
> throughput hits the bandwidth of the network, messages/second start 
> dropping, while megabits/second will remain constant.
> 
> > Oh and yeah.. ~30 us latency with a stock 2.6.27 kernel (that's a _tenth_
> > of Java-to-Rabbit??) and >600 MB throughput over loopback is nothing short
> > of awesome, considering this is on my 6 years old single-core box.
> > Great job!
> 
> Thanks!
> 
> Btw, 2.6.25 kernel showed some performance decrease and thus we've 
> sticked with 2.6.24 for our tests. It would be interesting to know 
> whether 2.6.27 fixes it and performs the same (or better) than 2.6.24...
> 
> Martin
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