Virtual interfaces performance

sa6kad · 10-31-2014, 05:01 AM

Hi. I am relatively new to Linux, but currently i am working on my thesis that requires some measurements and experiments of Linux performance while using hundreds (even thousands) virtual interfaces. My current task is to find out...
"1. How long does it take for kernel to (1) start and (2) shutdown a virtual interface? For that purpose, I would write a script that sequentially starts and shutdowns, say, 1000 virtual interfaces and observe the start/shutdown durations. Among these 1000 samples, I'd calculate the min/max/avg/stddev. I'd repeat the same experiment, but instead of sequentially spawning interfaces, this time I'd spawn them using 2, 3, 4, and so on threads. This way, I'd be able to observe the kernel's performance under concurrent load."

I wrote a simple script that starts N interfaces and assigns IP address to them:

Code:

echo "Enter number of interfaces: "
read int
a=8 #I use 10.0.0.0/20 network, but here i start from 10.0.8.0
b=2 #Physical interface has address 10.0.8.1, so virtual starts from 10.0.8.2

for (( i=1; i<=$int; i++ ))
do
	ifconfig eth2:$i 10.0.$a.$b/20 
	
		if [ $b -eq 255 ] #incrementing third octet of the IP address when forth reaches 255
		then ((a++))
			b=0
		else (( b++ ))		
		fi
	
done

Similar script stops all the interfaces when needed with the following code:

Code:

ifconfig eth2:$i down

So, my questions are:
1. How to measure this:

Quote:

sequentially starts and shutdowns, say, 1000 virtual interfaces and observe the start/shutdown durations

2. How to do this part:

Quote:

but instead of sequentially spawning interfaces, this time I'd spawn them using 2, 3, 4, and so on threads

3. What tools, techniques to use to observe/measure this:

Quote:

...to observe the kernel's performance under concurrent load.

Thank you.

Guttorm · 10-31-2014, 01:05 PM

Hi

Remember a script is interpreted, and running commands take time. So to get more sensible numbers, you need to run your script again where the ifconfig comand does nothing. You could change the ifconfig command to "ifconfig >/dev/null" and compare the results.

You can't use proper threads in a script. But adding & after the ifconfig command will start it in the background. After the loop is finished add a "wait" command, so it waits until all are done.

To measure things, you can use the command "time". If you want to time many commands, you can add () around a section to measure

Code:

time (
 command1
 command2
)

sa6kad · 11-01-2014, 05:22 AM

Quote:

Remember a script is interpreted, and running commands take time. So to get more sensible numbers, you need to run your script again where the ifconfig command does nothing. You could change the ifconfig command to "ifconfig >/dev/null" and compare the results.

Thank you. Yes, this was my next question: whether it makes sense to measure how much time it takes for the script to simply iterate N times and exclude this time from the time needed for the script to create/delete N virtual interfaces.

Another my question is how precise is time command. It provides time in milliseconds, however, if it gives a result of 0.001, is it literally 1 millisecond or it is a rounded value?

Could you elaborate on this, please:

Quote:

You can't use proper threads in a script

Guttorm · 11-01-2014, 08:01 AM

Code:

man time

http://stackoverflow.com/questions/2...s-and-a-thread