Performance Problems

Performance Problems

Diagnose CPU, memory, and system load issues.

Quick Overview

# System snapshot
uptime
free -h
vmstat 1 5

# Top processes
top -bn1 | head -20

High CPU Usage

Identify CPU Hogs

# Top by CPU
ps aux --sort=-%cpu | head -10

# Real-time
top -o %CPU

# Per-CPU view
mpstat -P ALL 1 5

# Process CPU history
pidstat 1 5

Diagnose Process

# Process details
ps -p PID -o pid,ppid,%cpu,%mem,cmd

# What's the process doing?
strace -p PID -c

# Threads
ps -T -p PID

CPU Information

# CPU info
lscpu
cat /proc/cpuinfo | grep "model name" | head -1

# Load averages explained
# 1-min, 5-min, 15-min averages
# Values > number of CPUs = overloaded
uptime
nproc  # Number of CPUs

High Memory Usage

Check Memory

# Memory overview
free -h

# Detailed
cat /proc/meminfo

# Per-process
ps aux --sort=-%mem | head -10

# Real-time
top -o %MEM

Memory Hogs

# Top memory users
ps aux --sort=-rss | head -10

# Specific process
pmap -x PID

# Shared memory
ipcs -m

Memory Issues

# OOM killer activity
dmesg | grep -i "out of memory"
journalctl -k | grep -i oom

# Swap usage
swapon --show
vmstat 1 5  # si/so columns

# Cache/buffers (usually OK to use)
free -h  # buff/cache column

High Load Average

Understanding Load

# Load average
uptime
cat /proc/loadavg

# Number of runnable processes
vmstat 1 5  # r column

# What's in run queue
ps -eo state,pid,cmd | grep "^R"

Common Causes

# I/O wait (blocked on disk)
vmstat 1 5  # wa column
iostat -x 1 5

# CPU bound
mpstat 1 5  # %usr high

# Too many processes
ps aux | wc -l

System Diagnostics

vmstat Explained

vmstat 1 5
# r: running processes
# b: blocked processes
# si/so: swap in/out (bad if high)
# us: user CPU %
# sy: system CPU %
# id: idle %
# wa: I/O wait % (bad if high)

sar (Historical)

# Install sysstat
sudo apt install sysstat

# CPU history
sar -u

# Memory history
sar -r

# I/O history
sar -b

Quick Fixes

CPU

# Kill runaway process
kill -9 PID

# Lower priority
renice 19 -p PID

# Limit CPU with cgroups
sudo cgcreate -g cpu:/limited
echo 50000 | sudo tee /sys/fs/cgroup/cpu/limited/cpu.cfs_quota_us
sudo cgclassify -g cpu:limited PID

Memory

# Clear caches (usually not needed)
sync && echo 3 | sudo tee /proc/sys/vm/drop_caches

# Kill memory hog
kill -9 PID

# Adjust OOM score
echo -1000 | sudo tee /proc/PID/oom_score_adj  # Protect
echo 1000 | sudo tee /proc/PID/oom_score_adj   # Target

Diagnostic Summary