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Thu, 9 Feb 2023 14:50:22 +0000 (GMT) Received: from smtpav07.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 94F3720040; Thu, 9 Feb 2023 14:50:21 +0000 (GMT) Received: from li-7e0de7cc-2d9d-11b2-a85c-de26c016e5ad.ibm.com (unknown [9.171.156.204]) by smtpav07.fra02v.mail.ibm.com (Postfix) with ESMTP; Thu, 9 Feb 2023 14:50:21 +0000 (GMT) Message-ID: Subject: Re: [PATCH v15 10/11] qapi/s390x/cpu topology: CPU_POLARITY_CHANGE qapi event From: Nina Schoetterl-Glausch To: Pierre Morel , Markus Armbruster 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, seiden@linux.ibm.com, nrb@linux.ibm.com, frankja@linux.ibm.com, berrange@redhat.com, clg@kaod.org Date: Thu, 09 Feb 2023 15:50:21 +0100 In-Reply-To: <517b73a9-51a5-53ab-538e-58bfb2cf20ae@linux.ibm.com> References: <20230201132051.126868-1-pmorel@linux.ibm.com> <20230201132051.126868-11-pmorel@linux.ibm.com> <5b26ee514ccbbfaf5670cbf0cb006d8e706fe5ae.camel@linux.ibm.com> <87y1p8q7v6.fsf@pond.sub.org> <32389178edcf67ac08904906df9a12aa64f24928.camel@linux.ibm.com> <517b73a9-51a5-53ab-538e-58bfb2cf20ae@linux.ibm.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.46.3 (3.46.3-1.fc37) MIME-Version: 1.0 X-TM-AS-GCONF: 00 X-Proofpoint-GUID: 9wqlhC_eM7SNKZEOjrMmdIwcarkdik_b X-Proofpoint-ORIG-GUID: fiL4LVnDo1_BKXxbOF3QQvqa-ggVpqif X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.219,Aquarius:18.0.930,Hydra:6.0.562,FMLib:17.11.170.22 definitions=2023-02-09_10,2023-02-09_03,2023-02-09_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 phishscore=0 suspectscore=0 spamscore=0 impostorscore=0 adultscore=0 mlxlogscore=999 mlxscore=0 clxscore=1015 bulkscore=0 malwarescore=0 lowpriorityscore=0 priorityscore=1501 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2212070000 definitions=main-2302090138 Received-SPF: pass client-ip=148.163.158.5; envelope-from=nsg@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 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-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Thu, 2023-02-09 at 14:00 +0100, Pierre Morel wrote: >=20 > On 2/9/23 13:28, Nina Schoetterl-Glausch wrote: > > On Wed, 2023-02-08 at 20:23 +0100, Markus Armbruster wrote: > > > Nina Schoetterl-Glausch writes: > > >=20 >=20 > ... >=20 > >=20 > > >=20 > > > > I also wonder if you should add 'feature' : [ 'unstable' ]. > > > > On the upside, it would mark the event as unstable, but I don't kno= w what the > > > > consequences are exactly. > > >=20 > > > docs/devel/qapi-code-gen.rst: > > >=20 > > > Special features > > > ~~~~~~~~~~~~~~~~ > > >=20 > > > Feature "deprecated" marks a command, event, enum value, or stru= ct > > > member as deprecated. It is not supported elsewhere so far. > > > Interfaces so marked may be withdrawn in future releases in acco= rdance > > > with QEMU's deprecation policy. > > >=20 > > > Feature "unstable" marks a command, event, enum value, or struct > > > member as unstable. It is not supported elsewhere so far. Inte= rfaces > > > so marked may be withdrawn or changed incompatibly in future rel= eases. > >=20 > > Yeah, I saw that, but wasn't aware of -compat, thanks. > >=20 > > >=20 > > > See also -compat parameters unstable-input, unstable-output, both > > > intended for "testing the future". > > >=20 > > > > Also I guess one can remove qemu events without breaking backwards = compatibility, > > > > since they just won't be emitted? Unless I guess you specify that a= event must > > > > occur under certain situations and the client waits on it? > > >=20 > > > Events are part of the interface just like command returns are. Not > > > emitting an event in a situation where it was emitted before can easi= ly > > > break things. Only when the situation is no longer possible, the eve= nt > > > can be removed safely. > >=20 > > @Pierre, seems it would be a good idea to mark all changes to qmp unsta= ble, not just > > set-cpu-topology, can just remove it later after all. >=20 > OK. >=20 > Just curious: how do you think this simple event matching the guest=20 > request 1 on 1 may evolve? Well, I don't know really, making it unstable is just more conservative for= now. But this way you can prototype/implement support in libvirt for topology an= d then make the interface stable one you've confirmed that everything works as int= ended. Here is something to think about: The architecture allows rejection of the = PTF polarization change request, if a request is currently in process. A possib= le design to allow the same semantics for qemu/libvirt would be to set a polarization= _change_in_progess bit when a PTF request occurs and refuse subsequent requests until this bit= was reset via qmp. This wouldn't result in the event data structure being changed, but its sem= antics, since it isn't fired for every request anymore. >=20 > Regards, > Pierre >=20