diff options
Diffstat (limited to 'doc/manual')
| -rw-r--r-- | doc/manual/advanced-topics/advanced-topics.xml | 1 | ||||
| -rw-r--r-- | doc/manual/advanced-topics/cores-vs-jobs.xml | 121 | ||||
| -rw-r--r-- | doc/manual/command-ref/conf-file.xml | 22 |
3 files changed, 137 insertions, 7 deletions
diff --git a/doc/manual/advanced-topics/advanced-topics.xml b/doc/manual/advanced-topics/advanced-topics.xml index 1b8841ad21c7..871b7eb1d37b 100644 --- a/doc/manual/advanced-topics/advanced-topics.xml +++ b/doc/manual/advanced-topics/advanced-topics.xml @@ -7,6 +7,7 @@ <title>Advanced Topics</title> <xi:include href="distributed-builds.xml" /> +<xi:include href="cores-vs-jobs.xml" /> <xi:include href="diff-hook.xml" /> <xi:include href="post-build-hook.xml" /> diff --git a/doc/manual/advanced-topics/cores-vs-jobs.xml b/doc/manual/advanced-topics/cores-vs-jobs.xml new file mode 100644 index 000000000000..eba645faf879 --- /dev/null +++ b/doc/manual/advanced-topics/cores-vs-jobs.xml @@ -0,0 +1,121 @@ +<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> diff --git a/doc/manual/command-ref/conf-file.xml b/doc/manual/command-ref/conf-file.xml index e818a74cd400..f3c721c783f2 100644 --- a/doc/manual/command-ref/conf-file.xml +++ b/doc/manual/command-ref/conf-file.xml @@ -238,8 +238,9 @@ false</literal>.</para> linkend='opt-cores'>--cores</option> command line switch and defaults to <literal>1</literal>. The value <literal>0</literal> means that the builder should use all available CPU cores in the - system.</para></listitem> + system.</para> + <para>See also <xref linkend="chap-tuning-cores-and-jobs" />.</para></listitem> </varlistentry> <varlistentry xml:id="conf-diff-hook"><term><literal>diff-hook</literal></term> @@ -482,8 +483,10 @@ builtins.fetchurl { <varlistentry xml:id="conf-max-free"><term><literal>max-free</literal></term> - <listitem><para>This option defines after how many free bytes to stop collecting - garbage once the <literal>min-free</literal> condition gets triggered.</para></listitem> + <listitem><para>When a garbage collection is triggered by the + <literal>min-free</literal> option, it stops as soon as + <literal>max-free</literal> bytes are available. The default is + infinity (i.e. delete all garbage).</para></listitem> </varlistentry> @@ -498,7 +501,10 @@ builtins.fetchurl { regardless). It can be overridden using the <option linkend='opt-max-jobs'>--max-jobs</option> (<option>-j</option>) - command line switch.</para></listitem> + command line switch.</para> + + <para>See also <xref linkend="chap-tuning-cores-and-jobs" />.</para> + </listitem> </varlistentry> <varlistentry xml:id="conf-max-silent-time"><term><literal>max-silent-time</literal></term> @@ -524,9 +530,11 @@ builtins.fetchurl { <varlistentry xml:id="conf-min-free"><term><literal>min-free</literal></term> <listitem> - <para>When the disk reaches <literal>min-free</literal> bytes of free disk space during a build, nix - will start to garbage-collection until <literal>max-free</literal> bytes are available on the disk. - A value of <literal>0</literal> (the default) means that this feature is disabled.</para> + <para>When free disk space in <filename>/nix/store</filename> + drops below <literal>min-free</literal> during a build, Nix + performs a garbage-collection until <literal>max-free</literal> + bytes are available or there is no more garbage. A value of + <literal>0</literal> (the default) disables this feature.</para> </listitem> </varlistentry> |