How about parsing the output from mpstat
from the sysstat
package? You can get statistics for each processor and set the interval (below is for 2s interval).
Sample output:
$ mpstat -P ALL 2
Linux 3.5.0-19-generic (ubuntu) 11/30/2012 _x86_64_ (4 CPU)
08:34:28 AM CPU %usr %nice %sys %iowait %irq %soft %steal %guest %idle
08:34:30 AM all 1.01 0.00 1.26 0.00 0.00 0.13 0.00 0.00 97.61
08:34:30 AM 0 2.50 0.00 1.50 0.00 0.00 0.50 0.00 0.00 95.50
08:34:30 AM 1 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00
08:34:30 AM 2 1.01 0.00 3.02 0.00 0.00 0.00 0.00 0.00 95.98
08:34:30 AM 3 0.50 0.00 0.50 0.00 0.00 0.00 0.00 0.00 99.00
Alternatively, you could implement the algorithm yourself. Take a look here and here.
Another way to do it would be to monitor the difference in idle time vs other usage time in /proc/stat
at defined time interval and calculate the load based on that. Here's more info on /proc/stat.