I've been using nmon & the analyser to investigate slow job turnaround times for jobs executed on a client system (a dedicated 9133-55A).
I've noticed high instances of IOWAIT over a period that corresponds quite nicely with two busy disks. So far, so good.
Now I want to nail down the specific processes in wait.
The TOP sheet in the nmon analyser output file shows the "big hitters" in terms of CPU%. (We are using the default threshold of 0.1% for identifying a "big" process)
In all cases, the (%user CPU + %sys CPU) = %CPU, suggesting that none of these processes is waiting.
My question is ... are waiting processes discarded/ignored by nmon ?
Thanks and regards,
nagger 100000MRSJ1688 Posts
Re: nmon TOP and waiting processes2013-03-25T22:51:37ZThis is the accepted answer. This is the accepted answer.Hi,
You have funny ideas about Wait stats.
Processes in "wait" are not using the CPU and are not on the run queue - they are asleep waiting on an interrupt queue (see ps -el WCHAN column).
CPU Wait time is actually CPU idle time but with the waiting for disks I/O to return flag set.
So no CPU is actually being used - actually it has to be doing something and that is running the wait process or yeilding a shared CPU to another LPAR and really not using the CPU.
This Wait time is calculated against the CPUs during clock interrupts and not individual processes - because they are not doing anything.
Processes not using CPU time in User mode (the application code) or System mode (running kernel system calls for the process) will be ignored, if they use less than the CPU threshold.
Cheers, Nigel Griffiths