Learn Understand first, then practice while the concept is still fresh.

M22 - Performance Diagnosis

Check CPU, memory, and disk pressure more systematically so a slow system is diagnosed from evidence instead of guesses.

Processes

Performance Diagnosis

Check CPU, memory, and disk pressure more systematically so a slow system is diagnosed from evidence instead of guesses.

45 min INTERMEDIATE BOTH Field-verified
Prerequisites
Module M18 - Process Model: What Processes Are Module M20 - Process Management: CLI Module M21 - Background and Foreground
What you should be able to do after this
  • Separate CPU pressure from memory pressure and disk pressure.
  • Use a few basic tools to inspect each area.
  • Avoid changing system settings before understanding the bottleneck.

Why This Matters

When a system feels slow, people often jump straight to a favorite explanation.

Real diagnosis is calmer than that. You want to ask:

  • is the CPU busy?
  • is memory tight or swapping?
  • is disk activity the bottleneck?

Those questions lead to better decisions than guessing from one symptom.

1. CPU Is Only One Part of the Story

High CPU can matter, but it does not automatically explain everything.

A system can also feel slow because:

  • memory pressure causes swapping or paging
  • storage is busy and processes are waiting on I/O
  • one stuck process is creating pressure for everything else

That is why you should not stop at one number.

2. Basic Memory Checks

Basic Memory Counters

Get-Counter “\Memory\Available MBytes” Get-Counter “\Memory\Pages/sec”

Basic Memory Checks

free -h cat /proc/meminfo | head -n 10

The goal is not to memorize every field. It is to notice whether free or available memory is very tight and whether swapping or paging activity seems significant.

3. Basic Disk and I/O Checks

If a process is waiting on storage, the system may feel slow even without dramatic CPU use.

Resource Monitor can be a practical visual starting point on Windows, especially for disk activity.

Open Resource Monitor

resmon

On Linux, top can hint at I/O wait, and tools such as iostat can provide a clearer storage picture if available.

I/O-Oriented Checks

top iostat -xz 1

A process can be “slow” because it is waiting, not because it is doing heavy compute.

4. Do Not Tune Blindly

It is tempting to jump to actions such as forcing kills, changing swap configuration, or installing tuning tools immediately.

That is rarely the right first move.

Better Performance Habit

Measure first. Identify which resource is under pressure. Change one thing only after you can explain why that change matches the evidence.

A Simple Diagnosis Sequence

  1. check overall system activity
  2. identify whether CPU, memory, or disk looks most stressed
  3. find the process or service contributing to that pressure
  4. only then decide whether to stop, tune, or defer work

That sequence is more valuable than memorizing lots of advanced counters.

What to Ignore for Now

  • deep kernel scheduler details
  • advanced storage tuning
  • container and cgroup performance internals

The goal here is learning how not to guess.

Before You Move On

You are ready for the process lab when you can:

  1. name the three main resource areas to inspect
  2. explain why a slow system is not always a CPU problem
  3. describe a calm first-pass diagnosis sequence

Next, we apply this in a process troubleshooting scenario.