On Wed, Jun 13, 2018 at 06:21:58PM +0000, Moger, Babu wrote: > > > > -----Original Message----- > > From: Eduardo Habkost [mailto:ehabk...@redhat.com] > > Sent: Wednesday, June 13, 2018 1:18 PM > > To: Moger, Babu <babu.mo...@amd.com> > > Cc: m...@redhat.com; marcel.apfelb...@gmail.com; pbonz...@redhat.com; > > r...@twiddle.net; mtosa...@redhat.com; qemu-devel@nongnu.org; > > k...@vger.kernel.org; k...@tripleback.net; ge...@hostfission.com; Jiri > > Denemark <jdene...@redhat.com> > > Subject: Re: [PATCH v13 3/5] i386: Enable TOPOEXT feature on AMD EPYC > > CPU > > > > On Wed, Jun 13, 2018 at 06:10:30PM +0000, Moger, Babu wrote: > > > > -----Original Message----- > > > > From: Eduardo Habkost [mailto:ehabk...@redhat.com] > > > > Sent: Wednesday, June 13, 2018 12:18 PM > > > > To: Moger, Babu <babu.mo...@amd.com> > > > > Cc: m...@redhat.com; marcel.apfelb...@gmail.com; > > pbonz...@redhat.com; > > > > r...@twiddle.net; mtosa...@redhat.com; qemu-devel@nongnu.org; > > > > k...@vger.kernel.org; k...@tripleback.net; ge...@hostfission.com; Jiri > > > > Denemark <jdene...@redhat.com> > > > > Subject: Re: [PATCH v13 3/5] i386: Enable TOPOEXT feature on AMD EPYC > > > > CPU > > > > > > > > On Wed, Jun 13, 2018 at 04:52:18PM +0000, Moger, Babu wrote: > > > > [...] > > > > > > What do you think our options are here? > > > > > > > > > > Should we drop automatic topoext completely and move forward? > > > > > What are your thoughts? > > > > > > > > Let's drop automatic topoext by now, and see if we find solutions > > > > later. I don't want to hold the rest of the patches because of > > > > this. > > > > > > Ok. I will drop topoext. > > > > > > > > > > > I'm thinking we could simply make kvm_arch_get_supported_cpuid() > > > > always return TOPOEXT on AMD CPUs, because the feature flag don't > > > > really depend on any KVM code to work (is that correct?). > > > > > > Yes, that is correct. I don't see any dependent code on TOPOEXT in KVM > > driver. > > > > > > Ok. Let me add TOPOEXT flag for all the AMD cpus and see how it goes. > > > > Hmm, this could actually solve all of our problems, then: > > > > We can forget about auto-topoext: just add TOPOEXT in > > kvm_arch_get_supported_cpuid(), add TOPOEXT unconditionally to > > the CPU models where you are interested into (EPYC only?), and > > add topoext=off to pc-2.12 compat_props. > > > > Ok Sure.
Sorry, I forgot we still need to decide what to do if TOPOEXT is enabled in the CPU model (or command-line) but the -smp options are not compatible with it. In other words, what should guest see on CPUID if using: "-machine pc-q35-3.0 -cpu EPYC -smp 64,cores=64" or: "-machine pc-q35-3.0 -cpu Opteron_G5,+topoext -smp 64,cores=64" I wonder what would happen if we just return zeroes on CPUID[0x800001E] if !topology_supports_topoext(), instead of trying to clear/set TOPOEXT depending on the -smp option? It would make things much simpler for QEMU and libvirt. -- Eduardo
