CPU Usage Versus Run Queue Length

[Salman Ahmed Qureshi]

Hi,
Can anyone please explain the relationship between CPU usage and run queue length? I have a 4 CPU machine where i see the run queue length 6 but the CPU usage is around 80 - 90 percent. According to my knowledge, if i have average run queue length of 4, it means 4 processes are waiting for their turn and ideally CPU should be 100% utilized at that time, am i right? Please correct me and give some good knowledge about this topic.
Thanks

[P Muralidhar Kini]

Hi Salman,

The following thread should help you-
http://forums13.itrc.hp.com/service/forums/questionanswer.do?admit=109447627+1277258604276+28353475&threadId=1311763

Hope this helps.

Regards,
Murali

[Kranti Mahmud]

Hi Salman,

The CPU Usage metric provides information about the percentage of time the CPU was in various states, for example, idle state and wait state. The metric also provides information about the percentage of CPU time spent in user and system mode. All data is per-CPU in a multi-CPU system.

CPU Run Queue Length is the number of ready threads in the processor queue. There is a single queue for processor time even on computers with multiple processors. A sustained processor queue of less than 10 threads per processor is normally acceptable, dependent on the workload.

Check the below links for more info:

http://docs.hp.com/en/B3921-90010/sar.1M.html
http://www.circle4.com/jaqui/papers/webunuk.html



Rgds-Kranti