linuxexpert-practice-labs/labs/linux-plus/5-5-1-cpu-memory-performance

Linux+ 5.5.1: CPU and memory performance

A baseline with sar, a CPU bottleneck, a process that switches context all the time, and a slow boot.

Before you start

The lab installs sysstat with collection off, starts two services that load this VM in different ways, and adds a unit that slows the boot. Reboot once after setup, so that the last boot includes it. Write answers to the files in /root/lab-answers/.

Tasks

1. Take a baseline (nproc, uptime, free -h, vmstat 1 3, sar -u 1 3), and turn on sysstat's collection so that sar has history, now and at boot.
2. Something keeps a CPU busy. Find the service behind it, write its name to /root/lab-answers/2, and stop it for good.
3. Count context switches per process (pidstat -w). One process switches thousands of times a second while using little CPU: write its name (the command pidstat shows) to /root/lab-answers/3.
4. Find the unit that slowed the last boot most, and write its name to /root/lab-answers/4. Look at the critical chain too.

Hints

• systemctl enable --now sysstat; on Ubuntu, also ENABLED="true" in /etc/default/sysstat.
• vmstat 1 5, uptime, mpstat -P ALL 1 1, top; ps -o unit= -p PID; systemctl disable --now.
• pidstat -w 1 3: the cswch/s column.
• systemd-analyze blame, systemd-analyze critical-chain.