mirror of
https://github.com/privatevoid-net/nix-super.git
synced 2024-11-23 22:46:16 +02:00
121 lines
3.7 KiB
XML
121 lines
3.7 KiB
XML
<chapter xmlns="http://docbook.org/ns/docbook"
|
||
xmlns:xlink="http://www.w3.org/1999/xlink"
|
||
xmlns:xi="http://www.w3.org/2001/XInclude"
|
||
version="5.0"
|
||
xml:id="chap-tuning-cores-and-jobs">
|
||
|
||
<title>Tuning Cores and Jobs</title>
|
||
|
||
<para>Nix has two relevant settings with regards to how your CPU cores
|
||
will be utilized: <xref linkend="conf-cores" /> and
|
||
<xref linkend="conf-max-jobs" />. This chapter will talk about what
|
||
they are, how they interact, and their configuration trade-offs.</para>
|
||
|
||
<variablelist>
|
||
<varlistentry>
|
||
<term><xref linkend="conf-max-jobs" /></term>
|
||
<listitem><para>
|
||
Dictates how many separate derivations will be built at the same
|
||
time. If you set this to zero, the local machine will do no
|
||
builds. Nix will still substitute from binary caches, and build
|
||
remotely if remote builders are configured.
|
||
</para></listitem>
|
||
</varlistentry>
|
||
<varlistentry>
|
||
<term><xref linkend="conf-cores" /></term>
|
||
<listitem><para>
|
||
Suggests how many cores each derivation should use. Similar to
|
||
<command>make -j</command>.
|
||
</para></listitem>
|
||
</varlistentry>
|
||
</variablelist>
|
||
|
||
<para>The <xref linkend="conf-cores" /> setting determines the value of
|
||
<envar>NIX_BUILD_CORES</envar>. <envar>NIX_BUILD_CORES</envar> is equal
|
||
to <xref linkend="conf-cores" />, unless <xref linkend="conf-cores" />
|
||
equals <literal>0</literal>, in which case <envar>NIX_BUILD_CORES</envar>
|
||
will be the total number of cores in the system.</para>
|
||
|
||
<para>The total number of consumed cores is a simple multiplication,
|
||
<xref linkend="conf-cores" /> * <envar>NIX_BUILD_CORES</envar>.</para>
|
||
|
||
<para>The balance on how to set these two independent variables depends
|
||
upon each builder's workload and hardware. Here are a few example
|
||
scenarios on a machine with 24 cores:</para>
|
||
|
||
<table>
|
||
<caption>Balancing 24 Build Cores</caption>
|
||
<thead>
|
||
<tr>
|
||
<th><xref linkend="conf-max-jobs" /></th>
|
||
<th><xref linkend="conf-cores" /></th>
|
||
<th><envar>NIX_BUILD_CORES</envar></th>
|
||
<th>Maximum Processes</th>
|
||
<th>Result</th>
|
||
</tr>
|
||
</thead>
|
||
<tbody>
|
||
<tr>
|
||
<td>1</td>
|
||
<td>24</td>
|
||
<td>24</td>
|
||
<td>24</td>
|
||
<td>
|
||
One derivation will be built at a time, each one can use 24
|
||
cores. Undersold if a job can’t use 24 cores.
|
||
</td>
|
||
</tr>
|
||
|
||
<tr>
|
||
<td>4</td>
|
||
<td>6</td>
|
||
<td>6</td>
|
||
<td>24</td>
|
||
<td>
|
||
Four derivations will be built at once, each given access to
|
||
six cores.
|
||
</td>
|
||
</tr>
|
||
<tr>
|
||
<td>12</td>
|
||
<td>6</td>
|
||
<td>6</td>
|
||
<td>72</td>
|
||
<td>
|
||
12 derivations will be built at once, each given access to six
|
||
cores. This configuration is over-sold. If all 12 derivations
|
||
being built simultaneously try to use all six cores, the
|
||
machine's performance will be degraded due to extensive context
|
||
switching between the 12 builds.
|
||
</td>
|
||
</tr>
|
||
<tr>
|
||
<td>24</td>
|
||
<td>1</td>
|
||
<td>1</td>
|
||
<td>24</td>
|
||
<td>
|
||
24 derivations can build at the same time, each using a single
|
||
core. Never oversold, but derivations which require many cores
|
||
will be very slow to compile.
|
||
</td>
|
||
</tr>
|
||
<tr>
|
||
<td>24</td>
|
||
<td>0</td>
|
||
<td>24</td>
|
||
<td>576</td>
|
||
<td>
|
||
24 derivations can build at the same time, each using all the
|
||
available cores of the machine. Very likely to be oversold,
|
||
and very likely to suffer context switches.
|
||
</td>
|
||
</tr>
|
||
</tbody>
|
||
</table>
|
||
|
||
<para>It is up to the derivations' build script to respect
|
||
host's requested cores-per-build by following the value of the
|
||
<envar>NIX_BUILD_CORES</envar> environment variable.</para>
|
||
|
||
</chapter>
|