Top and load average in Linux

It always practice to see top command output in the linux servers to identify the resource utilization.

We try to check load average and assume the performence of the system.

The top output looks like below

load average: 2.39, 1.70, 1.81

The same can be checked from 
$ cat  /proc/loadavg
2.70 2.45 2.13 1/450 6959

What are these 3 number?  how to analyze them ? What should be normal numbers?

The load average is computed based on CPU utilization, and includes the number of processes using or waiting to use the CPU,

The load average can be interpreted on a basic level as being a CPU core at full utilization has a system load average of one.

For a quad-core (4 core) machine, a system load average of 4 would mean that the machine had adequate resources to handle the work it needed to do, 

On the same quad-core system, a load average of 8 would mean that if the server had eight cores instead of four, 

It would have been able to handle the work, but it is now overloaded. 

So when you check load average, You also need to check the no of CPU cores on the server.

Use the below command to check the number of CPU cores on the server.

$ grep 'process' /proc/cpuinfo | wc -l
8

So the thumb rule is always load average should be less than the number of CPU (Cores), For 4 core server, Load average should be less than 4 always.


In case the system is showing high load average, but the CPU system and user utilization is low, it is time to start looking at IO wait.

IO wait shows up in system load on Linux because one or more of the cores is busy waiting on something having to do with either disk, or network input or output to finish before it can continue. 

Will post more on the IO waits and finding the IO issues in the next post.