When a system shows sluggish performance, we are examining Load average which reports some value. For a long time I was wondering how these values are actually calculated and what should be the ideal value for a given Linux server.
After some serious search, I found this article which gives satisfactory explanation on Load average.
After some serious search, I found this article which gives satisfactory explanation on Load average.
http://www.linuxjournal.com/article/9001
A simple version of the above given article is given in this URL:
A simple version of the above given article is given in this URL:
For people who don’t have time to go through these articles, here is the summary:
1. Load average NOT to be confused with CPU percentage.
2. Optimal Load average equals your number of CPU Cores.
“The point of perfect utilization, meaning that the CPUs are always busy and, yet, no process ever waits for one, is the average matching the number of CPUs. If there are four CPUs on a machine and the reported one-minute load average is 4.00, the machine has been utilizing its processors perfectly for the last 60 seconds. This understanding can be extrapolated to the 5- and 15-minute averages.”
“The point of perfect utilization, meaning that the CPUs are always busy and, yet, no process ever waits for one, is the average matching the number of CPUs. If there are four CPUs on a machine and the reported one-minute load average is 4.00, the machine has been utilizing its processors perfectly for the last 60 seconds. This understanding can be extrapolated to the 5- and 15-minute averages.”
3. Load average is good for getting a general feeling of the server's condition, but isn't the whole picture.
To make it further simple, if you have 8 CPU Cores (can be found using cat /proc/cpuinfo) on a Linux server, the ideal Load average should be around 8 (+/- 1). If its > 8, then the server resources are over-utilized and if < 8, the server isn’t running with its full potential.
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