docs/specs/rapl-msr.rst

12 Thanks to KVM's `MSR filtering <msr-filter-patch_>`__ functionality,
13 not all MSRs are handled by KVM. Some of them can now be handled by the
14 userspace (QEMU); a list of MSRs is given at VM creation time to KVM, and
17 .. _msr-filter-patch: https://patchwork.kernel.org/project/kvm/patch/20200916202951.23760-7-graf@am…
37 it with the UNIT provided above you'll get the power in micro-joules. This
45 core that belongs to PKG-0 will not be able to get the value of PKG-1 and
46 vice-versa.
49 -------------------------
51 In order to update the value of the virtual MSR, a QEMU thread is created.
54 1. Snapshot of the time metrics of all QEMU threads (Time spent scheduled in
58    the QEMU threads are running on.
60 3. Sleep for 1 second - During this pause the vcpu and other non-vcpu threads
64    time spent scheduled for each QEMU thread *and* the energy spent by the
67 5. Filter the vcpu threads and the non-vcpu threads.
72 7. The total energy spent by the non-vcpu threads is divided by the number
74    energy spent by the QEMU workers.
87 -----------------
101 .. _stat: https://man7.org/linux/man-pages/man5/proc.5.html
116 -----
119 mounted and available in the sysfs. if not, QEMU fails at start-up.
121 This feature is activated with -accel
122 kvm,rapl=true,rapl-helper-socket=/path/sock.sock
125 :program:`qemu-vmsr-helper` is listening to.
127 qemu-vmsr-helper
128 ----------------
130 The qemu-vmsr-helper is working very much like the qemu-pr-helper. Instead of
131 making persistent reservation, qemu-vmsr-helper is here to overcome the
132 CVE-2020-8694 which remove user access to the rapl msr attributes.
134 A socket communication is established between QEMU processes that has the RAPL
135 MSR support activated and the qemu-vmsr-helper. A systemd service and socket
136 activation is provided in contrib/systemd/qemu-vmsr-helper.(service/socket).
138 The systemd socket uses 600, like contrib/systemd/qemu-pr-helper.socket. The
140 changed (e.g. 660 and root:kvm for a Debian system for example). Libvirt could
144 See the qemu-pr-helper documentation or manpage for further details.
147 -------------------
149 - Works only on Intel host CPUs because AMD CPUs are using different MSR
152 - Only the Package Power-Plane (MSR_PKG_ENERGY_STATUS) is reported at the