1==================================
2QEMU virtual RAPL MSR helper
3==================================
4
5Synopsis
6--------
7
8**qemu-vmsr-helper** [*OPTION*]
9
10Description
11-----------
12
13Implements the virtual RAPL MSR helper for QEMU.
14
15Accessing the RAPL (Running Average Power Limit) MSR enables the RAPL powercap
16driver to advertise and monitor the power consumption or accumulated energy
17consumption of different power domains, such as CPU packages, DRAM, and other
18components when available.
19
20However those registers are accessible under privileged access (CAP_SYS_RAWIO).
21QEMU can use an external helper to access those privileged registers.
22
23:program:`qemu-vmsr-helper` is that external helper; it creates a listener
24socket which will accept incoming connections for communication with QEMU.
25
26If you want to run VMs in a setup like this, this helper should be started as a
27system service, and you should read the QEMU manual section on "RAPL MSR
28support" to find out how to configure QEMU to connect to the socket created by
29:program:`qemu-vmsr-helper`.
30
31After connecting to the socket, :program:`qemu-vmsr-helper` can
32optionally drop root privileges, except for those capabilities that
33are needed for its operation.
34
35:program:`qemu-vmsr-helper` can also use the systemd socket activation
36protocol.  In this case, the systemd socket unit should specify a
37Unix stream socket, like this::
38
39    [Socket]
40    ListenStream=/var/run/qemu-vmsr-helper.sock
41
42Options
43-------
44
45.. program:: qemu-vmsr-helper
46
47.. option:: -d, --daemon
48
49  run in the background (and create a PID file)
50
51.. option:: -q, --quiet
52
53  decrease verbosity
54
55.. option:: -v, --verbose
56
57  increase verbosity
58
59.. option:: -f, --pidfile=PATH
60
61  PID file when running as a daemon. By default the PID file
62  is created in the system runtime state directory, for example
63  :file:`/var/run/qemu-vmsr-helper.pid`.
64
65.. option:: -k, --socket=PATH
66
67  path to the socket. By default the socket is created in
68  the system runtime state directory, for example
69  :file:`/var/run/qemu-vmsr-helper.sock`.
70
71.. option:: -T, --trace [[enable=]PATTERN][,events=FILE][,file=FILE]
72
73  .. include:: ../qemu-option-trace.rst.inc
74
75.. option:: -u, --user=USER
76
77  user to drop privileges to
78
79.. option:: -g, --group=GROUP
80
81  group to drop privileges to
82
83.. option:: -h, --help
84
85  Display a help message and exit.
86
87.. option:: -V, --version
88
89  Display version information and exit.
90