Understanding Linux Load Average – Part 3

The Dutch Prutser's Blog

In part 1 we performed a series of experiments to explore the relation between CPU utilization and Linux load average. We concluded that the load average is influenced by processes running on or waiting for the CPU. Based on experiments in part 2 we came to the conclusion that processes that are performing disk I/O also influence the load average on a Linux system. In this posting we will do another experiment to find out if the Linux load average is also affected by processes performing network I/O.

Network I/O and load average

To check if a correlation exists between processes performing network I/O and the load average we will start 10 processes generating network I/O on an otherwise idle system and collect various performance related statistics using the sar command. Note: My load-gen script uses the ping command to generate network I/O.

The above output shows that the lo

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Understanding Linux Load Average – Part 2

The Dutch Prutser's Blog

In part 1 we performed a series of experiments to explore the relation between CPU utilization and Linux load average. We came to the conclusion that CPU utilization clearly influences the load average. In part 2 we will continue our experiments and take a look if disk I/O also influences the Linux load average.

Disk I/O and load average

The first experiment is starting 2 processes performing disk I/O on an otherwise idle system to measure the amount I/O issued, the load average and CPU utilization using the sar command. BTW: My load-gen script uses the dd command to generate disk I/O.

The -b command line option given to sar tells it to report disk I/O statistics. The above output tells us that on average 48207 blocks per second were written to disk and almost nothing was read. What effect does this have on the load average?

The run-queue utilization…

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Understanding Linux Load Average – Part 1

Very nice article on how to detect load average issue

The Dutch Prutser's Blog

A frequently asked question in my classroom is “What is the meaning of load average and when is it too high?”. This may sound like an easy question, and I really thought it was, but recently I discovered that things aren’t always that easy as they seem. In this first of a three-part post I will explain what the meaning of Linux load average is and how to diagnose load averages that may seem too high.

Obtaining the current load average is very simple by issuing the uptime command:

But what is the meaning of these 3 numbers? Basically load average is the run-queue utilization averaged over the last minute, the last 5 minutes and the last 15 minutes. The run-queue is a list of processes waiting for a resource to become available inside the Linux operating system. The example above indicates that on average there were 10.52 processes waiting…

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