Part II · Your system

18. CPU

hub

What your processor is, how busy it is, and who keeps it busy.

$ atfq cpu
  CPU       11th Gen Intel(R) Core(TM) i7-1165G7 @ 2.80GHz · 8 logical CPUs
  Load      1.25, 0.90, 0.62 over 1, 5 and 15 minutes, for 8 CPUs
  Tasks     2 running right now, 1043 in all
  Governor  powersave

Commands

nproc

number of CPUs you can use

lscpu

model, cores, threads and caches

uptime

load average over 1, 5 and 15 minutes 18.1

top

busiest processes; press 1 for one line per CPU

mpstat -P ALL 1

usage of each CPU every second (package sysstat)

Paths

/proc/cpuinfo

one block per logical CPU

/proc/loadavg

load average and task counts

/sys/devices/system/cpu/

online CPUs, frequency, governor

Cards

1. 18.1Load averageLoad average: the number of tasks running or waiting for a CPU, plus those waiting on disk (D state), averaged over 1, 5 and 15 minutes.

Also about this

1. 1.2How the kernel shares the CPUsThere are more tasks wanting a CPU than CPUs, so the scheduler gives each a short turn, then switches: a context switch.
2. 1.4Interrupts: how devices get attentionA device that needs the CPU (a packet arrived, a disk finished, a key was pressed) raises an interrupt: the CPU stops what it's doing and runs the kernel's handler for that device.
3. 2.2Cores, threads and socketsA core is a complete processor. A chip (package, or socket) holds several; a server board can hold several chips.
4. 2.3CPU caches: why memory layout mattersRAM is about 100 times slower than the CPU's own registers. Small, fast memories in the chip keep recent data close: L1 (tens of KiB per core, a few cycles), L2 (MiB, about a dozen cycles), L3 (shared, tens of cycles).
5. 2.4Clock speed, turbo and power savingA CPU's speed changes all the time: it climbs when there's work, drops when idle, and goes above its base frequency (turbo) while power and heat allow.
6. 16.3nice and prioritiesNiceness goes from -20 (greedy) to 19 (polite). The default is 0.