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Fri, 15 Jul 2022 09:11:15 +0000 (GMT) Received: from [9.171.51.176] (unknown [9.171.51.176]) by b06wcsmtp001.portsmouth.uk.ibm.com (Postfix) with ESMTP; Fri, 15 Jul 2022 09:11:12 +0000 (GMT) Message-ID: Date: Fri, 15 Jul 2022 11:11:12 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.10.0 Subject: Re: [PATCH v8 08/12] s390x/cpu_topology: implementing numa for the s390x topology Content-Language: en-US To: Pierre Morel , 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, frankja@linux.ibm.com References: <20220620140352.39398-1-pmorel@linux.ibm.com> <20220620140352.39398-9-pmorel@linux.ibm.com> <3a821cd1-b8a0-e737-5279-8ef55e58a77f@linux.ibm.com> From: Janis Schoetterl-Glausch In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: hgKtMTsKQuZmqD2EcPXJ_zBlpy1RLD2G X-Proofpoint-ORIG-GUID: TcOnVhb8sBU0OLgraX7h4gTRw2hvtzXS X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.205,Aquarius:18.0.883,Hydra:6.0.517,FMLib:17.11.122.1 definitions=2022-07-15_03,2022-07-14_01,2022-06-22_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 lowpriorityscore=0 adultscore=0 malwarescore=0 suspectscore=0 mlxscore=0 phishscore=0 bulkscore=0 impostorscore=0 spamscore=0 mlxlogscore=999 clxscore=1015 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2206140000 definitions=main-2207150039 Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On 7/14/22 22:17, Pierre Morel wrote: > > > On 7/14/22 16:57, Janis Schoetterl-Glausch wrote: >> On 6/20/22 16:03, Pierre Morel wrote: >>> S390x CPU Topology allows a non uniform repartition of the CPU >>> inside the topology containers, sockets, books and drawers. >>> >>> We use numa to place the CPU inside the right topology container >>> and report the non uniform topology to the guest. >>> >>> Note that s390x needs CPU0 to belong to the topology and consequently >>> all topology must include CPU0. >>> >>> We accept a partial QEMU numa definition, in that case undefined CPUs >>> are added to free slots in the topology starting with slot 0 and going >>> up. >> >> I don't understand why doing it this way, via numa, makes sense for us. >> We report the topology to the guest via STSI, which tells the guest >> what the topology "tree" looks like. We don't report any numa distances to the guest. >> The natural way to specify where a cpu is added to the vm, seems to me to be >> by specify the socket, book, ... IDs when doing a device_add or via -device on >> the command line. >> >> [...] >> > > It is a choice to have the core-id to determine were the CPU is situated in the topology. > > But yes we can chose the use drawer-id,book-id,socket-id and use a core-id starting on 0 on each socket. > > It is not done in the current implementation because the core-id implies the socket-id, book-id and drawer-id together with the smp parameters. > > Regardless of whether the core-id or the combination of socket-id, book-id .. is used to specify where a CPU is located, why use the numa framework and not just device_add or -device ? That feels way more natural since it should already just work if you can do hotplug. At least with core-id and I suspect with a subset of your changes also with socket-id, etc. Whereas numa is an awkward fit since it's for specifying distances between nodes, which we don't do, and you have to use a hack to get it to specify which CPUs to plug (via setting arch_id to -1).