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Mon, 5 Sep 2022 15:24:00 +0000 (GMT) Received: from d06av22.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 36BC64C044; Mon, 5 Sep 2022 15:24:00 +0000 (GMT) Received: from li-7e0de7cc-2d9d-11b2-a85c-de26c016e5ad.ibm.com (unknown [9.171.44.172]) by d06av22.portsmouth.uk.ibm.com (Postfix) with ESMTP; Mon, 5 Sep 2022 15:24:00 +0000 (GMT) Message-ID: <6d779ae286bd24a76e6cc4b2cc4dcaafdf9acf75.camel@linux.ibm.com> Subject: Re: [PATCH v9 01/10] s390x/cpus: Make absence of multithreading clear From: Janis Schoetterl-Glausch To: Pierre Morel , Nico Boehr , 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, frankja@linux.ibm.com Date: Mon, 05 Sep 2022 17:23:59 +0200 In-Reply-To: References: <20220902075531.188916-1-pmorel@linux.ibm.com> <20220902075531.188916-2-pmorel@linux.ibm.com> <166237756810.5995.16085197397341513582@t14-nrb> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.42.4 (3.42.4-2.fc35) MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: vBHXs-Ej_Hu-q9cxIVDhS7C_LBT_4-Vf X-Proofpoint-GUID: FPx6Jz7d1Nu1H68ucsV7qRojRCo2v4X0 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.205,Aquarius:18.0.895,Hydra:6.0.528,FMLib:17.11.122.1 definitions=2022-09-05_09,2022-09-05_03,2022-06-22_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 malwarescore=0 spamscore=0 lowpriorityscore=0 mlxlogscore=999 suspectscore=0 phishscore=0 adultscore=0 clxscore=1015 bulkscore=0 priorityscore=1501 mlxscore=0 impostorscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2207270000 definitions=main-2209050072 Received-SPF: pass client-ip=148.163.158.5; envelope-from=scgl@linux.ibm.com; helo=mx0a-001b2d01.pphosted.com X-Spam_score_int: -19 X-Spam_score: -2.0 X-Spam_bar: -- X-Spam_report: (-2.0 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Mon, 2022-09-05 at 17:10 +0200, Pierre Morel wrote: > > On 9/5/22 13:32, Nico Boehr wrote: > > Quoting Pierre Morel (2022-09-02 09:55:22) > > > S390x do not support multithreading in the guest. > > > Do not let admin falsely specify multithreading on QEMU > > > smp commandline. > > > > > > Signed-off-by: Pierre Morel > > > --- > > > hw/s390x/s390-virtio-ccw.c | 3 +++ > > > 1 file changed, 3 insertions(+) > > > > > > diff --git a/hw/s390x/s390-virtio-ccw.c b/hw/s390x/s390-virtio-ccw.c > > > index 70229b102b..b5ca154e2f 100644 > > > --- a/hw/s390x/s390-virtio-ccw.c > > > +++ b/hw/s390x/s390-virtio-ccw.c > > > @@ -86,6 +86,9 @@ static void s390_init_cpus(MachineState *machine) > > > MachineClass *mc = MACHINE_GET_CLASS(machine); > > > int i; > > > > > > + /* Explicitely do not support threads */ > > ^ > > Explicitly > > > > > + assert(machine->smp.threads == 1); > > > > It might be nicer to give a better error message to the user. > > What do you think about something like (broken whitespace ahead): > > > > if (machine->smp.threads != 1) {if (machine->smp.threads != 1) { > > error_setg(&error_fatal, "More than one thread specified, but multithreading unsupported"); > > return; > > } > > > > > OK, I think I wanted to do this and I changed my mind, obviously, I do > not recall why. > I will do almost the same but after a look at error.h I will use > error_report()/exit() instead of error_setg()/return as in: > > > + /* Explicitly do not support threads */ > + if (machine->smp.threads != 1) { > + error_report("More than one thread specified, but > multithreading unsupported"); > + exit(1); > + } I agree that an assert is not a good solution, and I'm not sure aborting is a good idea either. I'm assuming that currently if you specify threads > 0 qemu will run with the number of CPUs multiplied by threads (compared to threads=1). If that is true, then a new qemu version will break existing invocations. An alternative would be to print a warning and do: cores *= threads threads = 1 The questions would be what the best place to do that is. I guess we'd need a new compat variable if that's done in machine-smp.c > > > Thanks, > > Regards, > Pierre >