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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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