topic Re: Disk IO and run queue length in Operating System - HP-UX

Disk IO and run queue length

Salman Ahmed Qureshi — Mon, 26 Jul 2010 01:38:41 GMT

Hi,
If a process is waiting for disk IO con complete, is it added to the run queue length? For example, if on a 2 CPU machine, if there are two processes are waiting for CPU and 2 are waiting for IO to complete before asking from the CPU tipe, would run queue length be 4 in this case? or Run queue lenght is calculate only on the bases of the processes waiting for the CPU?
Thanks

Re: Disk IO and run queue length

DeafFrog — Mon, 26 Jul 2010 03:18:55 GMT

V. Salom ,
On HP-UX 11i, this does not include processes/threads that are waiting for IO to complete, i.e., high-priority sleepers. On previous versions of HP-UX, the Load Average included hi-priority sleepers , and as such the Average load shown might not be accurate.
Regards,
TheFrogIsDeaf.

Re: Disk IO and run queue length

Salman Ahmed Qureshi — Mon, 26 Jul 2010 04:34:08 GMT

Any idea about AIX? It on a 4 CPU machine, it shows me load average of 7 but CPU usage is around 80%

Re: Disk IO and run queue length

muruganantham raju — Tue, 27 Jul 2010 03:20:30 GMT

Hi,
The processes waiting for IO will not accounted for CPU RUN QUEUE calculation. The process is mainly blocked for disk activity and not for CPU.

In AIX, how many physical processors are there in the system? If it is 4, then you might have enable multithreading in which case the total processors are 8. Load average of 7 is not accounting for 100% CPU utilization.

HTH
Muru