> -----Original Message----- > From: Eduardo Habkost [mailto:ehabkost@xxxxxxxxxx] > Sent: Wednesday, June 13, 2018 1:49 PM > To: Moger, Babu <Babu.Moger@xxxxxxx> > Cc: mst@xxxxxxxxxx; marcel.apfelbaum@xxxxxxxxx; pbonzini@xxxxxxxxxx; > rth@xxxxxxxxxxx; mtosatti@xxxxxxxxxx; qemu-devel@xxxxxxxxxx; > kvm@xxxxxxxxxxxxxxx; kash@xxxxxxxxxxxxxx; geoff@xxxxxxxxxxxxxxx; Jiri > Denemark <jdenemar@xxxxxxxxxx> > Subject: Re: [PATCH v13 3/5] i386: Enable TOPOEXT feature on AMD EPYC > CPU > > On Wed, Jun 13, 2018 at 06:21:58PM +0000, Moger, Babu wrote: > > > > > > > -----Original Message----- > > > From: Eduardo Habkost [mailto:ehabkost@xxxxxxxxxx] > > > Sent: Wednesday, June 13, 2018 1:18 PM > > > To: Moger, Babu <Babu.Moger@xxxxxxx> > > > Cc: mst@xxxxxxxxxx; marcel.apfelbaum@xxxxxxxxx; > pbonzini@xxxxxxxxxx; > > > rth@xxxxxxxxxxx; mtosatti@xxxxxxxxxx; qemu-devel@xxxxxxxxxx; > > > kvm@xxxxxxxxxxxxxxx; kash@xxxxxxxxxxxxxx; geoff@xxxxxxxxxxxxxxx; Jiri > > > Denemark <jdenemar@xxxxxxxxxx> > > > 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:ehabkost@xxxxxxxxxx] > > > > > Sent: Wednesday, June 13, 2018 12:18 PM > > > > > To: Moger, Babu <Babu.Moger@xxxxxxx> > > > > > Cc: mst@xxxxxxxxxx; marcel.apfelbaum@xxxxxxxxx; > > > pbonzini@xxxxxxxxxx; > > > > > rth@xxxxxxxxxxx; mtosatti@xxxxxxxxxx; qemu-devel@xxxxxxxxxx; > > > > > kvm@xxxxxxxxxxxxxxx; kash@xxxxxxxxxxxxxx; geoff@xxxxxxxxxxxxxxx; > Jiri > > > > > Denemark <jdenemar@xxxxxxxxxx> > > > > > 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. Yes. I have kept that check. But, I had to implement topology_supports_topoext bit differently. Reason for this is we need to disable this feature before the x86_cpu_expand_features. But problem is nr_cores and nr_threads are not populated at this time. It is populated in qemu_init_vcpus. Please take a look at topology_supports_topoext again. > > 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" > Tested both these cases. It works fine with some warning messages. > 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. I did not see that difference in behavior if we clear the bit versus return 0s. Sending new patches now. Please review. One note: I will going on vacation from June 20th for couple of weeks. If possible I would like to close this feature. If we cannot that is fine. Just an FYI. > > -- > Eduardo
