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Thu, 8 Dec 2022 09:44:36 +0000 (GMT) From: Pierre Morel To: qemu-s390x@nongnu.org Cc: qemu-devel@nongnu.org, borntraeger@de.ibm.com, pasic@linux.ibm.com, richard.henderson@linaro.org, david@redhat.com, thuth@redhat.com, cohuck@redhat.com, mst@redhat.com, pbonzini@redhat.com, kvm@vger.kernel.org, ehabkost@redhat.com, marcel.apfelbaum@gmail.com, eblake@redhat.com, armbru@redhat.com, seiden@linux.ibm.com, nrb@linux.ibm.com, scgl@linux.ibm.com, frankja@linux.ibm.com, berrange@redhat.com, clg@kaod.org Subject: [PATCH v13 7/7] docs/s390x: document s390x cpu topology Date: Thu, 8 Dec 2022 10:44:32 +0100 Message-Id: <20221208094432.9732-8-pmorel@linux.ibm.com> X-Mailer: git-send-email 2.31.1 In-Reply-To: <20221208094432.9732-1-pmorel@linux.ibm.com> References: <20221208094432.9732-1-pmorel@linux.ibm.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: LYdLbaQtXdsdPJ9IKDCUqK5lywi98jhi X-Proofpoint-ORIG-GUID: Xec_YaXbKLzt6rfLXJMBDnEdpcgvdywQ X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.205,Aquarius:18.0.923,Hydra:6.0.545,FMLib:17.11.122.1 definitions=2022-12-08_04,2022-12-07_01,2022-06-22_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1015 mlxlogscore=999 malwarescore=0 spamscore=0 mlxscore=0 lowpriorityscore=0 priorityscore=1501 bulkscore=0 impostorscore=0 phishscore=0 adultscore=0 suspectscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2210170000 definitions=main-2212080077 Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org Add some basic examples for the definition of cpu topology in s390x. Signed-off-by: Pierre Morel --- docs/system/s390x/cpu-topology.rst | 87 ++++++++++++++++++++++++++++++ docs/system/target-s390x.rst | 1 + 2 files 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..12f974cc54 --- /dev/null +++ b/docs/system/s390x/cpu-topology.rst @@ -0,0 +1,87 @@ +CPU Topology on s390x +===================== + +CPU Topology on S390x provides up to 5 levels of topology containers: +nodes, drawers, books, sockets and CPUs. +While the 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 parent container. + +Currently QEMU CPU topology uses a single level of container: the sockets. + +For backward compatibility, threads can be declared on the ``-smp`` command +line. They will be seen as CPUs by the guest as long as multithreading +is not really supported by QEMU for S390. + +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 +of QEMU, we use a capability, ``KVM_CAP_S390_CPU_TOPOLOGY``, to notify KVM +QEMU use of the CPU Topology. + +Enabling CPU topology +--------------------- + +Currently, CPU topology is only enabled in the host model. + +Enabling CPU topology in a CPU model is done by setting the CPU flag +``ctop`` to ``on`` like in: + +.. code-block:: bash + + -cpu gen16b,ctop=on + +Having the topology disabled by default allows migration between +old and new QEMU without adding new flags. + +Indicating the CPU topology to the Virtual Machine +-------------------------------------------------- + +The CPU Topology, can be specified on the QEMU command line +with the ``-smp`` or the ``-device`` QEMU command arguments. + +In the following machine we define 8 sockets with 4 cores each. +Note that S390 QEMU machines do not implement multithreading. + +.. code-block:: bash + + $ qemu-system-s390x -m 2G \ + -cpu gen16b,ctop=on \ + -smp cpus=5,sockets=8,cores=4,maxcpus=32 \ + -device host-s390x-cpu,core-id=14 \ + +New CPUs can be plugged using the device_add hmp command like in: + +.. code-block:: bash + + (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 up to maxcpus. + +In the example above: + +* There are 5 CPUs provided to the guest with the ``-smp`` command line + They will take the core-ids 0,1,2,3,4 + As we have 4 cores in a socket, we have 4 CPUs provided + to the guest in socket 0, with core-ids 0,1,2,3. + The last cpu, with core-id 4, will be on socket 1. + +* the core with ID 14 provided by the ``-device`` command line will + be placed in socket 3, with core-id 14 + +* the core with ID 9 provided by the ``device_add`` qmp command will + be placed in socket 2, with core-id 9 + +Note that the core ID is machine wide and the CPU TLE masks provided +by the STSI instruction will be writen in a big endian mask: + +* in socket 0: 0xf0000000 (core id 0,1,2,3) +* in socket 1: 0x08000000 (core id 4) +* in socket 2: 0x00400000 (core id 9) +* in socket 3: 0x00020000 (core id 14) diff --git a/docs/system/target-s390x.rst b/docs/system/target-s390x.rst index c636f64113..ff0ffe04f3 100644 --- a/docs/system/target-s390x.rst +++ b/docs/system/target-s390x.rst @@ -33,3 +33,4 @@ Architectural features .. toctree:: s390x/bootdevices s390x/protvirt + s390x/cpu-topology -- 2.31.1