Skip to content
ENExplore Calculators

Nice Priority Effect Calculator

Work out nice priority effect instantly with clear inputs, formula shown and shareable results.

About Nice Priority Effect Calculator

The Linux completely fair scheduler assigns each nice level a weight, where every step changes the weight by a factor of about 1.25. Ten nice levels of separation therefore gives roughly a nine-to-one CPU ratio, and twenty levels about eighty-to-one. Nice only matters when the CPU is contended; on an idle system it has no effect.

Formula

CFS weighting

weight = 1.25^(-nice); share = weight / sum of weights; each nice step changes CPU share by about 25 percent

Worked example

With the default values below, Nice Priority Effect Calculator returns CPU share of process A of 96.60%. Change any input above and every figure here is recalculated in your browser.

Inputs used

Nice value of process Aaccepts -20–19
-5
Nice value of process Baccepts -20–19
10
CPU cores availableminimum 1
4

Results

CPU share of process A
96.60%
CPU share of process B
3.40%
CPU ratio A to B
28.42 x
Core equivalents for process A
3.86

Step by step

  1. 1Values used
  2. 2CFS weighting
  3. 3CPU share of process A= 96.60
  4. 4CPU share of process B= 3.40
  5. 5CPU ratio A to B= 28.42 x
  6. 6Core equivalents for process A= 3.86

Assumptions and limits

  • The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Does nice guarantee a CPU share?

No, it is proportional weighting among runnable tasks. For a hard guarantee use cgroup CPU quotas, which cap and reserve rather than merely prioritise.

Why does nice not help my I/O-bound job?

Because it only affects CPU scheduling. Use ionice with the CFQ or BFQ I/O scheduler to prioritise disk access.

Related Calculators

Nice Priority Effect Calculator | Calcrivo