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[213.175.37.10]) by smtp.gmail.com with ESMTPSA id my14-20020a1709065a4e00b006f3ef214dc5sm6066300ejc.43.2022.05.10.04.37.59 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 10 May 2022 04:37:59 -0700 (PDT) Date: Tue, 10 May 2022 13:37:58 +0200 From: Igor Mammedov To: "Daniel P. =?UTF-8?B?QmVycmFuZ8Op?=" Cc: Suravee Suthikulpanit , qemu-devel@nongnu.org, marcel.apfelbaum@gmail.com, mst@redhat.com, pbonzini@redhat.com, richard.henderson@linaro.org, eduardo@habkost.net, jon.grimm@amd.com, Julia Suvorova Subject: Re: [PATCH] pc: q35: Bump max_cpus to 512 Message-ID: <20220510133758.5495372c@redhat.com> In-Reply-To: References: <20220504131639.13570-1-suravee.suthikulpanit@amd.com> <20220509091249.392fdab6@redhat.com> <20220510090325.2781238a@redhat.com> X-Mailer: Claws Mail 4.0.0 (GTK+ 3.24.31; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Received-SPF: pass client-ip=170.10.133.124; envelope-from=imammedo@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -28 X-Spam_score: -2.9 X-Spam_bar: -- X-Spam_report: (-2.9 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.082, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, 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 Tue, 10 May 2022 09:14:19 +0100 Daniel P. Berrang=C3=A9 wrote: > On Tue, May 10, 2022 at 09:03:25AM +0200, Igor Mammedov wrote: > > On Mon, 9 May 2022 13:03:38 +0100 > > Daniel P. Berrang=C3=A9 wrote: > > =20 > > > On Mon, May 09, 2022 at 09:12:49AM +0200, Igor Mammedov wrote: =20 > > > > On Wed, 4 May 2022 08:16:39 -0500 > > > > Suravee Suthikulpanit wrote: > > > > =20 > > > > > This is the maximum number of vCPU supported by > > > > > the AMD x2APIC virtualization. > > > > >=20 > > > > > Signed-off-by: Suravee Suthikulpanit > > > > > --- > > > > > hw/i386/pc_q35.c | 2 +- > > > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > >=20 > > > > > diff --git a/hw/i386/pc_q35.c b/hw/i386/pc_q35.c > > > > > index 302288342a..e82b1c690d 100644 > > > > > --- a/hw/i386/pc_q35.c > > > > > +++ b/hw/i386/pc_q35.c > > > > > @@ -357,7 +357,7 @@ static void pc_q35_machine_options(MachineCla= ss *m) > > > > > machine_class_allow_dynamic_sysbus_dev(m, TYPE_INTEL_IOMMU_D= EVICE); > > > > > machine_class_allow_dynamic_sysbus_dev(m, TYPE_RAMFB_DEVICE); > > > > > machine_class_allow_dynamic_sysbus_dev(m, TYPE_VMBUS_BRIDGE); > > > > > - m->max_cpus =3D 288; > > > > > + m->max_cpus =3D 512; =20 > > > >=20 > > > > Maybe we should bump it to KVM VCPU maximum, > > > > and make sure we error out if asked for combination of > > > > hardware/irqchip is not usable. =20 > > >=20 > > > In RHEL downstream we currently bump this to 710 CPUs, because you > > > overflow the SMBIOS 2.1 tables at approx 720 CPUs (give/take a little > > > depending on other config options). =20 > >=20 > > Also there were some testing done with 1024, > > but my main reason for matching KVM's limit is unblock upstream > > testing so it would be easier to push limits for others. > > Downstream can clamp that value down to whatever it deems as supported. > > =20 > > > Going beyond 710 CPUs value requires using the SMBIOS 3 entry point. > > >=20 > > > AFAIK, the x86 machine types still default to SMBIOS 2.1, so that > > > would need changing too. =20 > >=20 > > Yep, we can change default to SMBIOS 3 starting with new machine type (= 7.1?) > > or conditionally depending on requested number of CPUs, > > though I'd prefer machine type approach. =20 >=20 > Agree, machine type is better IMHO, a it gives us a consistent guest > ABI regardless of CPU count. >=20 > > As for SMBIOS 3, we still have to update CPU structures to support more= than > > 255 vcpus (Julia was working on it). It's long standing bug, but that d= oesn't > > seem to be critical, as guest boots fine with old structures. =20 >=20 > What's the impact of SMBIOS 3 being limited to 255 ? That's lower than > the current max CPUs of 288 in upstream / 710 in downstream. possibly users that look into SMBIOS for licensing purposes and/or inventory Julia told me that dmidecode somehow figures out correct number of total vc= pus. CCing Julia for patches ETA. >=20 >=20 > With regards, > Daniel