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Thu, 9 Feb 2023 12:12:17 +0000 (GMT) Message-ID: <4622b3c1e565b89132be8b5a8cda61aef9c5d0f6.camel@linux.ibm.com> Subject: Re: [PATCH v15 10/11] qapi/s390x/cpu topology: CPU_POLARITY_CHANGE qapi event From: Nina Schoetterl-Glausch To: "Daniel P." =?ISO-8859-1?Q?Berrang=E9?= Cc: Pierre Morel , 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, clg@kaod.org Date: Thu, 09 Feb 2023 13:12:17 +0100 In-Reply-To: References: <20230201132051.126868-1-pmorel@linux.ibm.com> <20230201132051.126868-11-pmorel@linux.ibm.com> <5b26ee514ccbbfaf5670cbf0cb006d8e706fe5ae.camel@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-ORIG-GUID: -JX1S8K_g0O9nBPlUzquX3j3ffVzMzJX X-Proofpoint-GUID: oNcO3-iylCci_b6u-xk_we-Ogsqhlehu X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.219,Aquarius:18.0.930,Hydra:6.0.562,FMLib:17.11.122.1 definitions=2023-02-09_08,2023-02-08_02,2022-06-22_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 mlxlogscore=999 priorityscore=1501 bulkscore=0 lowpriorityscore=0 suspectscore=0 spamscore=0 adultscore=0 clxscore=1015 phishscore=0 malwarescore=0 mlxscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2212070000 definitions=main-2302090115 Received-SPF: pass client-ip=148.163.156.1; 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, 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 10:04 +0000, Daniel P. Berrang=C3=A9 wrote: > On Wed, Feb 08, 2023 at 06:35:39PM +0100, Nina Schoetterl-Glausch wrote: > > On Wed, 2023-02-01 at 14:20 +0100, Pierre Morel wrote: > > > When the guest asks to change the polarity this change > > > is forwarded to the admin using QAPI. > > > The admin is supposed to take according decisions concerning > > > CPU provisioning. > > >=20 > > > Signed-off-by: Pierre Morel > > > --- > > > qapi/machine-target.json | 30 ++++++++++++++++++++++++++++++ > > > hw/s390x/cpu-topology.c | 2 ++ > > > 2 files changed, 32 insertions(+) > > >=20 > > > diff --git a/qapi/machine-target.json b/qapi/machine-target.json > > > index 58df0f5061..5883c3b020 100644 > > > --- a/qapi/machine-target.json > > > +++ b/qapi/machine-target.json > > > @@ -371,3 +371,33 @@ > > > }, > > > 'if': { 'all': [ 'TARGET_S390X', 'CONFIG_KVM' ] } > > > } > > > + > > > +## > > > +# @CPU_POLARITY_CHANGE: > > > +# > > > +# Emitted when the guest asks to change the polarity. > > > +# > > > +# @polarity: polarity specified by the guest > > > +# > > > +# The guest can tell the host (via the PTF instruction) whether the > > > +# CPUs should be provisioned using horizontal or vertical polarity. > > > +# > > > +# On horizontal polarity the host is expected to provision all vCPUs > > > +# equally. > > > +# On vertical polarity the host can provision each vCPU differently. > > > +# The guest will get information on the details of the provisioning > > > +# the next time it uses the STSI(15) instruction. > > > +# > > > +# Since: 8.0 > > > +# > > > +# Example: > > > +# > > > +# <- { "event": "CPU_POLARITY_CHANGE", > > > +# "data": { "polarity": 0 }, > > > +# "timestamp": { "seconds": 1401385907, "microseconds": 422329 = } } > > > +# > > > +## > > > +{ 'event': 'CPU_POLARITY_CHANGE', > > > + 'data': { 'polarity': 'int' }, > > > + 'if': { 'all': [ 'TARGET_S390X', 'CONFIG_KVM'] } > >=20 > > I wonder if you should depend on CONFIG_KVM or not. If tcg gets topolog= y > > support it will use the same event and right now it would just never be= emitted. > > On the other hand it's more conservative this way. > >=20 > > I also wonder if you should add 'feature' : [ 'unstable' ]. > > On the upside, it would mark the event as unstable, but I don't know wh= at the > > consequences are exactly. >=20 > The intention of this flag is to allow mgmt apps to make a usage policy > decision. >=20 > Libvirt's policy is that we'll never use features marked unstable. Does it enforce that, e.g via compat policies? If so, I assume there is some way to allow use of unstable features in libv= irt for development? If for example you're prototyping a new mgmt feature that uses unstable com= mands. >=20 > IOW, the consequence of marking it unstable is that it'll likely > go unused until the unstable marker gets removed. >=20 > Using 'unstable' is useful if you want to get complex code merged > before you're quite happy with the design, and then iterate on the > impl in-tree. This is OK if there's no urgent need for apps to > consume the feature. If you want the feature to be used for real > though, the unstable flag is not desirable and you need to finalize > the design. >=20 > > Also I guess one can remove qemu events without breaking backwards comp= atibility, > > since they just won't be emitted? Unless I guess you specify that a eve= nt must > > occur under certain situations and the client waits on it? >=20 > As Markus says, that's not a safe assumption. If a mgmt app is expecting > to receive an event, ceasing to emit it would likely be considered a > regression. >=20 >=20 > With regards, > Daniel