CPU bottleneck & WCHAN

[Sundar_7]

I would like to know, on a nutshell, when we can determine if CPU is the bottlecheck ?

1) the load average displayed by uptime and top. Can we go by the assumption that if the number of processes in the run queue is more than 5, means the CPU is the bottleneck ? and also a considerable number of processes in the BLOCKED_ON_PRIORITY state means the CPU is the BN ?

2) Does anyone know the WCHAN value of the processes that are in the BLOCKED_ON_PRIORITY state ?

Thanks in advance

Sundar.

[Stefan Farrelly]

A general guideline is a load average of 1 per cpu is the max, ie. if 4 cpu's then a max load is 4. But - load average is influenced by all sorts of things, not just cpu, so its unreliable.

sar is much more reliable. Simply run it for quite a while;

sar 1 100

And if %idle is averaging 0 or 1% then you are completely out of cpu. the /usr/bin/top command is also helpful. But you may simply have a runaway process consuming your spare cpu - so be sure this is not the case first.

[Sundar_7]

My understanding is that we cannot really go by the sar -u output to determine if the CPU is bottleneck or not.

If the WIO is more say 60% the idle will be less than 10% (rest for USR & SYS), that doesnt mean CPU is the bottleneck ? Am I right here ?

[Sundar_7]

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