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 Post subject: Investigating Idlepc idlemax to minimise CPU usage
PostPosted: Sat Oct 22, 2011 6:03 am 

Joined: Fri Mar 05, 2010 11:33 am
Posts: 1494
Location: Australia
[Edit: Some useful background info can be found at topic6040.html (summary) or at ... d-finally/ (full Article)]
This is an extension to a previous article; "The Illusive Art of Acquiring A Good Idle-PC Value". Read it before you read this.

So - you have found a good idle-pc value, and are using it in your labs. But still your CPU is churning away at a rate higher than you'd like.

There may be a solution in sight yet - the idlepc idlemax setting.

Thanks to sharky1337 who alerted me to the possibility of adjusting the idlemax values, I found that others had already started giving advice here and here.

But these all talked about setting the idlemax value to 100. I wanted to see what other values would do.

How to set the idlemax value

Step 1:
Observe your CPU Utilisation

Windows: Open the windows task manager and sort by %CPU
Linux: Open a console window and enter the command top
Mac OS X: Open a terminal window and enter the command top -o cpu

Keep this window visible for the entire process.

Step 2:
Load your topology, or build a new one. I'm assuming you are already using the best idle-pc values you could find.

Start your routers. Control->Start/Resume...

Check your CPU utilisation. After peaking high, it should settle once all routers are started.

Wait for all routers to go green.

(TIP 1: If your routers take too long to start, or won't all start, try starting a few, set the idlemax as described below and continue starting a few at at a time)
TIP 2: Opening a console session can also cause the CPU utilisation to drop.

Now click in the Dynagen management console at the bottom of the page.
Enter the command:
idlepc idlemax /all 100

Check your CPU utilisation now. It will probably have dropped. If it hasn't dropped enough, you can try another value. eg:
idlepc idlemax /all 10

BUT before you get too carried away, you must realise that all this CPU saving comes at a cost.

Step 3:
Test your Console Access
Go to the console of one of your idlemax-tamed routers and issue a show run command from privileged mode.

If, (A) the console won't open, or (B) the output from your commands is slow, then tune your idlemax value up a bit higher. To put it back to the default:
idlepc idlemax /all 1500

While still at the Dynagen management console, check your settings by issuing a show run command. You should see something like:
=> show run
autostart = False
    workingdir = /opt/GNS3/Working
    udp = 10000
        image = /opt/GNS3/IOS/c3725-adventerprisek9-mz.124-15.T10.image
        ram = 256
        idlepc = 0x6026b804
        idlemax = 10
        ghostios = True

Step 4:
Saving your idlemax values
Nothign to it. Now that you have set the idlemax values, they will automatically be saved when you save your topology file. If you take a look at after saving your project, you should see the idlemax = xx line included.

Raw Data
For those who are interested, I conducted a barrage of tests on Macintosh OSX (GNS3 v0.7.4), Ubuntu (GNS3 0.8.1) and Windows 7 (GNS3 0.8.1). My raw results as I recorded them are in the attached file
idlemax.txt [11.87 KiB]
Downloaded 2294 times

GNS3 WorkBench-a VMware image of Ubuntu with GNS3 and VPCS installed and a collection of exercises/labs

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