doc: FAQ: Add info on IO and CPU prioritization

doc/faq.rst

@@ -49,3 +49,43 @@ implementing unattended backups happens in :issue:`533`.
                root).
 
 .. _accessible only to that user: https://security.stackexchange.com/questions/14000/environment-variable-accessibility-in-linux/14009#14009
+
+How to prioritize restic's IO and CPU time
+------------------------------------------
+
+If you'd like to change the **IO priority** of restic, run it in the following way
+
+::
+
+$ ionice -c2 -n0 ./restic -r /media/your/backup/ backup /home
+
+This runs ``restic`` in the so-called best *effort class* (``-c2``),
+with the highest possible priority (``-n0``).
+
+Take a look at the `ionice manpage`_ to learn about the other classes.
+
+.. _ionice manpage: https://linux.die.net/man/1/ionice
+
+
+To change the **CPU scheduling priority** to a higher-than-standard
+value, use would run:
+
+::
+
+$ nice --10 ./restic -r /media/your/backup/ backup /home
+
+Again, the `nice manpage`_ has more information.
+
+.. _nice manpage: https://linux.die.net/man/1/nice
+
+You can also **combine IO and CPU scheduling priority**:
+
+::
+
+$ ionice -c2 nice -n19 ./restic -r /media/gour/backup/ backup /home
+
+This example puts restic in the IO class 2 (best effort) and tells the CPU
+scheduling algorithm to give it the least favorable niceness (19).
+
+The above example makes sure that the system the backup runs on
+is not slowed down, which is particularly useful for servers.