Changeset a334dd2a

Timestamp:

02/13/2022 06:24:50 PM (2 years ago)

Author:

Pierre Labastie <pierre.labastie@…>

Branches:

11.1, 11.2, 11.3, 12.0, 12.1, kea, ken/TL2024, ken/inkscape-core-mods, ken/tuningfonts, lazarus, lxqt, plabs/newcss, plabs/python-mods, python3.11, qt5new, rahul/power-profiles-daemon, renodr/vulkan-addition, trunk, xry111/intltool, xry111/llvm18, xry111/soup3, xry111/test-20220226, xry111/xf86-video-removal

Children:

8e305cf

Parents:

dfe5714

git-author:

Pierre Labastie <pierre.labastie@…> (02/13/2022 06:19:19 PM)

git-committer:

Pierre Labastie <pierre.labastie@…> (02/13/2022 06:24:50 PM)

Message:

Building Notes: tell why the number of jobs may have to be limited

Also tell how to limit the number of jobs with ninja

File:

• introduction/important/building-notes.xml (modified) (4 diffs)

introduction/important/building-notes.xml

@@ -207 +207 @@
     <screen><userinput>make -j2</userinput></screen>
 
+    <para>
+      If you have applied the optional <command>sed</command> when building
+      <application>ninja</application> in LFS, you can use:
+    </para>
+
+    <screen><userinput>export NINJAJOBS=2</userinput></screen>
+
+    <para>
+      when a package uses <command>ninja</command>, or just:
+    </para>
+
+    <screen><userinput>ninja -j2</userinput></screen>
+
+    <para>
+      but for ninja, the default number of jobs is &lt;N&gt;+2, where &lt;N&gt;
+      is the number of processors available, so that using the above commands
+      is rather for limiting the number of jobs (see below for why this could
+      be necessary).
+    </para>
+
     <para>Generally the number of processes should not exceed the number of
     cores supported by the CPU.  To list the processors on your
@@ -212 +232 @@
     </para>
 
-    <para>In some cases, using multiple processors may result in a 'race'
+    <para>In some cases, using multiple processes may result in a 'race'
     condition where the success of the build depends on the order of the
     commands run by the <command>make</command> program.  For instance, if an
@@ -223 +243 @@
     <para>If this occurs, the best way to proceed is to drop back to a
     single processor build.  Adding '-j1' to a make command will override
-    the similar setting in the MAKEFLAGS environment variable.</para>
+    the similar setting in the <envar>MAKEFLAGS</envar> environment
+    variable.</para>
 
     <note><para>When running the package tests or the install portion of the
@@ -231 +252 @@
     that are difficult to debug.</para></note>
 
+    <important>
+      <para>
+        Another problem may occur with modern CPU's, which have a lot of cores.
+        Each job started consumes memory, and if the sum of the needed
+        memory for each job exceeds the available memory, you may encounter
+        either an OOM (Out of Memory) kernel interrupt or intense swapping
+        that will slow the build beyond reasonable limits.
+      </para>
+
+      <para>
+        Some compilations with <command>g++</command> may consume up to 2.5 GB
+        of memory, so to be safe, you should restrict the number of jobs
+        to (Total Memory in GB)/2.5, at least for big packages such as LLVM,
+        WebKitGtk, QtWebEngine, or libreoffice.
+      </para>
+    </important>
   </sect2>