From 15e3dedcee1d0830871ffc692143318a87646101 Mon Sep 17 00:00:00 2001
From: Christian Segundo
Date: Thu, 25 Jul 2024 02:12:22 +0200
Subject: wip

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+---
+layout: post
+title: Say goodbye to desktop lag while compiling your @world
+category: GNU/Linux
+tags:
+  - gentoo
+  - systemd
+---
+
+1. Start by creating a new systemd slice `/etc/systemd/system/portage.slice`:
+
+   ```
+   [Install]
+   WantedBy=slices.target
+
+   [Slice]
+   CPUShares=256
+   ```
+
+1. Enable and start the unit you just created:
+
+   ```
+   systemctl enable --now portage.slice
+   ```
+
+   CPUShares option defaults to 1024, `systemd` will create a user slice for
+   each user with an active session, and all processes that user run will be
+   assigned to that slice, anything that a user may run will receive 4 times the
+   CPU time of processes assigned to the portage slice.
+
+   ```
+   ➜  ~ cat /sys/fs/cgroup/cpu,cpuacct/user.slice/cpu.shares
+   1024
+   ```
+
+1. Repurpose `PORTAGE_IONICE_COMMAND` variable. This is one of those awesome
+   variables you can set in your `make.conf` to alter how you build stuff. It
+   should be a command string for portage to call to modify its own priority
+   with a `\${PID}` placeholder that will be substituted with a `PID`. Maybe it
+   was created with `ionice` in mind, but we can abuse that placeholder to write
+   pids to the `cgroup.procs` file in the portage slice.
+
+   Add the following line to your `/etc/portage/make.conf`:
+
+   ```
+   PORTAGE_IONICE_COMMAND="sh -c \"echo \${PID} > /sys/fs/cgroup/systemd/portage.slice/cgroup.procs\""
+   ```
+
+   The `cgroup.procs` file is present in every cgroup and contains a list of
+   processes that are members of that particular cgroup. Writing a PID to this
+   file will move all threads in that process at once to the cgroup. And that,
+   is awesome :D
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