Add some basic examples for the definition of cpu topology in s390x. Signed-off-by: Pierre Morel <pmorel@xxxxxxxxxxxxx> --- docs/system/s390x/cpu_topology.rst | 88 ++++++++++++++++++++++++++++++ 1 file changed, 88 insertions(+) create mode 100644 docs/system/s390x/cpu_topology.rst diff --git a/docs/system/s390x/cpu_topology.rst b/docs/system/s390x/cpu_topology.rst new file mode 100644 index 0000000000..00977d4319 --- /dev/null +++ b/docs/system/s390x/cpu_topology.rst @@ -0,0 +1,88 @@ +CPU Topology on s390x +===================== + +CPU Topology on S390x provides up to 4 levels of topology containers: +drawers, books, sockets and CPUs. +While the three higher level containers, Containers Topology List Entries, +(Containers TLE) define a tree hierarchy, the lowest level of topology +definition, the CPU Topology List Entry (CPU TLE), provides the placement +of the CPUs inside the last container. + +Prerequisites +------------- + +To use CPU Topology a Linux QEMU/KVM machine providing the CPU Topology facility +(STFLE bit 11) is required. + +However, since this facility has been enabled by default in an early version, +the capability ``KVM_CAP_S390_CPU_TOPOLOGY`` is needed to indicate to KVM +that QEMU support CPU Topology. + +Indicating the CPU topology to the Virtual Machine +-------------------------------------------------- + +The CPU Topology, number of drawers, number of books per drawers, number of +sockets per book and number of cores per sockets is specified with the +``-smp`` qemu command arguments. + +Like in : + +.. code-block:: sh + -smp cpus=1,drawers=3,books=4,sockets=2,cores=8,maxcpus=192 + +If drawers or books are not specified, their default to 1. + +New CPUs can be plugged using the device_add hmp command like in: + +.. code-block:: sh + (qemu) device_add host-s390x-cpu,core-id=9 + +The core-id defines the placement of the core in the topology by +starting with core 0 in socket 0, book 0 and drawer 0 up to the maximum +core number of the last socket of the last book in the last drawer. + +In the example above: + +* the core with ID 9 will be placed in container (0,0,1), as core 9 + of CPU TLE 0 of socket 1 in book 0 from drawer 0. +* the core ID 0 is defined by the -smp cpus=1 command and will be + placed as core 0 in CPU TLE 0 of container (0,0,0) + +Note that the core ID is machine wide and the CPU TLE masks provided +by the STSI instruction will be: + +* in socket 0: 0x80000000 (core id 0) +* in socket 1: 0x00400000 (core id 9) + +Indicating the CPU topology to the Guest +---------------------------------------- + +The guest can query for topology changes using the PTF instruction. +In case of a topology change it can request the new topology by issuing +STSI instructions specifying the level of detail required, drawer with +STSI(15.1.4) or books STSI(15.1.3). + +The virtual machine will fill the provided buffer with the count of +drawers (MAG4), books per drawer (MAG3), sockets per book (MAG2) and +cores per socket (MAG1). + +Note that the STSI(15.1.2) is special in two ways: + +* When the firmware detect a change in the values calculated for STSI(15.1.2) + it will trigger the report of the topology change for the PTF instruction. + +Migration +--------- + +For virtio-ccw machines older than s390-virtio-ccw-7.2, CPU Topoogy is +by default disabled. + +CPU Topoogy is by default enabled for s390-virtio-ccw-7.2 and newer machines. + +Enabling the CPU topology on older Machine is done by setting the global +option ''topology-disable'' to false before enabling cpu topology with the +cpu feature "ctop" like in: + +.. code-block:: sh + -machine s390-ccw-virtio-3.0,accel=kvm,topology-disable=false + -cpu z14,ctop=on -- 2.31.1
