Idle CPU and runqueue

[zeburocks]

Hello,

Can this be a possibility?.

Having free CPU cycles,but high runqueues?.

1. Sar -u, top and vmstat shows free cpu available. No IO waits.

2. But Runqueue is single digit (vmstat).

We do not have the above mentioned scenario, but we are trying to see if we can scale down the number of CPUs by increasing its speed. The current cpu utilization is around 30%. There is a fear that, we may not have CPUs to service concurrent requests even though we have free cpu cycles available, thus leading to runqueues.

If you think it is possible to get into such a scenario, can you provide me with some details?

Thanks

 

[marrow]

Hello zeburocks. As far as I was aware, if the run queue value is lower than the number of cpu's, you have no problems. This is from an old document I have: -

"It may depend on the number of cpu's in a system, therefore if r is >5 and only one cpu, not good, but if r >6 for two cpus this is acceptable. So in a 10 x cpu system with 30 processes waiting is ok.

By

 

[zeburocks]

Hi Marrow,

Yup. I got that part. Thanks !!

But, when I have free cpu cycles available (50% +), would I still see runqueues?. My understanding is No.

Thanks

 

[marrow]

Hello zeburocks

I've looked around 12-15 of our systems, r always = 0 with CPU lowest figure at +60%, so I can't find a 50%. Some questions: Have you run "uptime" - what does it say? And what exactly is the max. number vmstat "r" is showing, does it drop down to lower value i.e. "0" and how many cpu's do you have? I assume you use "prstat".

Marrow