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Mon, 10 Oct 2022 17:20:33 +0000 (GMT) Received: from d06av26.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id B0141AE051; Mon, 10 Oct 2022 17:20:32 +0000 (GMT) Received: from [9.171.50.118] (unknown [9.171.50.118]) by d06av26.portsmouth.uk.ibm.com (Postfix) with ESMTP; Mon, 10 Oct 2022 17:20:32 +0000 (GMT) Message-ID: <95d0c5d1-f623-c0a7-bcf6-9bb1fa71fdd4@linux.ibm.com> Date: Mon, 10 Oct 2022 19:20:32 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.3.1 Subject: Re: [PATCH v9 01/10] s390x/cpus: Make absence of multithreading clear To: =?UTF-8?Q?Daniel_P=2e_Berrang=c3=a9?= Cc: qemu-s390x@nongnu.org, 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, =?UTF-8?Q?C=c3=a9dric_Le_Goater?= References: <20220902075531.188916-1-pmorel@linux.ibm.com> <20220902075531.188916-2-pmorel@linux.ibm.com> Content-Language: en-US From: Pierre Morel In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: uJS5HPbcWPCOgoQ_bwTOKvwXn296G67X X-Proofpoint-ORIG-GUID: -iXfmWCf9CXYXmdjGd6Y2lisXqlEV1Wy 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=2022-10-10_10,2022-10-10_02,2022-06-22_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 phishscore=0 priorityscore=1501 impostorscore=0 mlxscore=0 mlxlogscore=999 adultscore=0 suspectscore=0 bulkscore=0 clxscore=1015 spamscore=0 malwarescore=0 lowpriorityscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2209130000 definitions=main-2210100101 Received-SPF: pass client-ip=148.163.158.5; envelope-from=pmorel@linux.ibm.com; helo=mx0b-001b2d01.pphosted.com X-Spam_score_int: -39 X-Spam_score: -4.0 X-Spam_bar: ---- X-Spam_report: (-4.0 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-2.007, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 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 9/28/22 20:11, Daniel P. Berrangé wrote: > On Fri, Sep 02, 2022 at 09:55:22AM +0200, Pierre Morel wrote: >> 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 */ >> + assert(machine->smp.threads == 1); > > What is the functional effect for currently released QEMU versions > if a user has set threads == 2 for an s390 machine ? Is the > threads setting simply ignored ? It is not ignored, the number of CPUs per sockets seen by the guest is cores*threads > > If we want to eliminate this mistake, then there's two possible > options > > * If it had no effect, treat this like a deprecation process > where we print a warning for 2 releases, and then turn the > warning into an error. Gives a little grace to fix the config > mistakes some users might have made, at a time convenient to > them. > > Or > > * If it had effect and we need migration compatibility then forbid > threads > 1 only for new machine type versions, so existing > deployed guests are not changed. > > With regards, > Daniel Thanks for your comments Daniel. I will need to forbid threads > 1 for new machine. regards, Pierre -- Pierre Morel IBM Lab Boeblingen