On Tue, May 10, 2022 at 09:03:25AM +0200, Igor Mammedov wrote: > On Mon, 9 May 2022 13:03:38 +0100 > Daniel P. Berrangé <berra...@redhat.com> wrote: > > > On Mon, May 09, 2022 at 09:12:49AM +0200, Igor Mammedov wrote: > > > On Wed, 4 May 2022 08:16:39 -0500 > > > Suravee Suthikulpanit <suravee.suthikulpa...@amd.com> wrote: > > > > > > > This is the maximum number of vCPU supported by > > > > the AMD x2APIC virtualization. > > > > > > > > Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpa...@amd.com> > > > > --- > > > > hw/i386/pc_q35.c | 2 +- > > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > > > 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(MachineClass *m) > > > > machine_class_allow_dynamic_sysbus_dev(m, TYPE_INTEL_IOMMU_DEVICE); > > > > machine_class_allow_dynamic_sysbus_dev(m, TYPE_RAMFB_DEVICE); > > > > machine_class_allow_dynamic_sysbus_dev(m, TYPE_VMBUS_BRIDGE); > > > > - m->max_cpus = 288; > > > > + m->max_cpus = 512; > > > > > > 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. > > > > 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). > > 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. > > > Going beyond 710 CPUs value requires using the SMBIOS 3 entry point. > > > > AFAIK, the x86 machine types still default to SMBIOS 2.1, so that > > would need changing too. > > 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.
Agree, machine type is better IMHO, a it gives us a consistent guest ABI regardless of CPU count. > 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 doesn't > seem to be critical, as guest boots fine with old structures. 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. With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
