On Thu, Aug 27, 2020 at 10:21:10PM +0200, Igor Mammedov wrote: > On Wed, 26 Aug 2020 13:45:51 -0500 > Babu Moger <babu.mo...@amd.com> wrote: > > > > > > > > -----Original Message----- > > > From: Dr. David Alan Gilbert <dgilb...@redhat.com> > > > Sent: Wednesday, August 26, 2020 1:34 PM > > > To: Moger, Babu <babu.mo...@amd.com> > > > Cc: Igor Mammedov <imamm...@redhat.com>; Daniel P. Berrangé > > > <berra...@redhat.com>; ehabk...@redhat.com; m...@redhat.com; Michal > > > Privoznik <mpriv...@redhat.com>; qemu-devel@nongnu.org; > > > pbonz...@redhat.com; r...@twiddle.net > > > Subject: Re: [PATCH v5 0/8] Remove EPYC mode apicid decode and use generic > > > decode > > > > > > * Babu Moger (babu.mo...@amd.com) wrote: > > > > > > > > > -----Original Message----- > > > > > From: Igor Mammedov <imamm...@redhat.com> > > > > > Sent: Wednesday, August 26, 2020 8:31 AM > > > > > To: Daniel P. Berrangé <berra...@redhat.com> > > > > > Cc: Moger, Babu <babu.mo...@amd.com>; pbonz...@redhat.com; > > > > > r...@twiddle.net; ehabk...@redhat.com; qemu-devel@nongnu.org; > > > > > m...@redhat.com; Michal Privoznik <mpriv...@redhat.com> > > > > > Subject: Re: [PATCH v5 0/8] Remove EPYC mode apicid decode and use > > > > > generic decode > > > > > > > > > > On Wed, 26 Aug 2020 13:50:59 +0100 > > > > > Daniel P. Berrangé <berra...@redhat.com> wrote: > > > > > > > > > > > On Wed, Aug 26, 2020 at 02:38:49PM +0200, Igor Mammedov wrote: > > > > > > > On Fri, 21 Aug 2020 17:12:19 -0500 Babu Moger > > > > > > > <babu.mo...@amd.com> wrote: > > > > > > > > > > > > > > > To support some of the complex topology, we introduced EPYC > > > > > > > > mode > > > > > apicid decode. > > > > > > > > But, EPYC mode decode is running into problems. Also it can > > > > > > > > become quite a maintenance problem in the future. So, it was > > > > > > > > decided to remove that code and use the generic decode which > > > > > > > > works for majority of the topology. Most of the SPECed > > > > > > > > configuration would work just fine. With some non-SPECed user > > > > > > > > inputs, it will create some sub- > > > > > optimal configuration. > > > > > > > > Here is the discussion thread. > > > > > > > > https://nam11.safelinks.protection.outlook.com/?url=https%3A%2 > > > > > > > > F%2F > > > > > > > > lore.kernel.org%2Fqemu-devel%2Fc0bcc1a6-1d84-a6e7-e468- > > > > > d5b437c1b25 > > > > > > > > > > > > > > > > 4%40amd.com%2F&data=02%7C01%7Cbabu.moger%40amd.com%7C8a5c > > > > > 52f92 > > > > > > > > > > > > > > > > 3f04082a40808d849c43d49%7C3dd8961fe4884e608e11a82d994e183d%7C0%7 > > > > > C0 > > > > > > > > > > > > > > > > %7C637340454473508873&sdata=VnW28H1v4XwK3GaNGFxu%2BhwiMeA > > > > > YO%2B > > > > > > > > 3WAzo3DeY5Ha8%3D&reserved=0 > > > > > > > > > > > > > > > > This series removes all the EPYC mode specific apicid changes > > > > > > > > and use the generic apicid decode. > > > > > > > > > > > > > > the main difference between EPYC and all other CPUs is that it > > > > > > > requires numa configuration (it's not optional) so we need an > > > > > > > extra > > > > No, That is not true. Because of that assumption we made all these > > > > apicid changes. And here we are now. > > > > > > > > AMD supports varies mixed configurations. In case of EPYC-Rome, we > > > > have NPS1, NPS2 and NPS4(Numa Nodes per socket). In case of NPS1, > > > > basically we have all the cores in a socket under one numa node. This > > > > is non-numa configuration. > > > > Looking at the various configurations and also discussing internally, > > > > it is not advisable to have (epyc && !numa) check. > > > > > > Indeed on real hardware, I don't think we always see NUMA; my single > > > socket, > > > 16 core/32 thread 7302P Dell box, shows the kernel printing 'No NUMA > > > configuration found...Faking a node.' > looks like firmware bug or maybe it's feature and there is a knob in fw > to turn it on/off in case used OS doesn't like it for some reason. > > > > > So if real hardware hasn't got a NUMA node, what's the real problem? > > > > I don't see any problem once we revert all these changes(patch 1-7). > > We don't need if (epyc && !numa) error check or auto_enable_numa=true > > unconditionally. > > We need revert to unbreak migration from QEMU < 5.0, > everything else (fixes for CPUID_Fn8000001E) could go on top. > > So what's on top (because old code also wasn't correct when > CPUID_Fn8000001E is taken in account, tha's why we are at this point), > > When starting QEMU without -numa > Indeed we can skip "if (epyc && !numa) error check or auto_enable_numa=true", > in case where there is 1 die (NPS1). > (1) User however may set core/threads number bigger than possible by spec, > in which case CPUID_Fn8000001E_EBX/CPUID_Fn8000001E_ECX will not be > valid spec vise and could trigger OPPs in guest kernel. > Given we allow go out of spec, perhaps we should add a warning at > realize time saying that used -smp config is not supported since it > doesn't match AMD EPYC spec and might not work. > > (2) Earlier we agreed that we can reuse existing die_id instead of internal > (topo_ids.node_id in current code) > (It's is called DIE_ID and NODE ID in spec interchangeably) > Same as (1) add a warning when '-smp dies' goes beyond spec limits. > > (3) "-smp dies>1" ''if'' we allow to run it without -numa, > then system wide NUMA node id in CPUID_Fn8000001E_ECX probably doesn't > matter. > could be something like in spec but taking in account die offset, to > produce > unique id. > > Same, add a warning that there are more than 1 dies but numa is not > enabled, > suggest to enable numa. > > With current code it produces invalid APIC ID for valid '-smp' > combination, > however if we revert it and switch to die_id than it should produce > valid APIC ID once again (as in 4.2). > Given it produces invalid APIC id, maybe we should just ditch the case and > fold it in (4) (i.e. require -numa if "-smp dies>1") > > (4) -numa is used (RHBZ1728166) > we need to ensure that socket*dies == ms->numa_state->num_nodes > and make sure that CPUID_Fn8000001E_ECX consistent with > cpu mapping provided with "-numa cpu=" option.
Why do we need to socket*dies == ms->numa_state->num_nodes ? That doesn't seem to be the case in bare metal EPYC nodes I've used which lets you configure how many NUMA nodes in firmware. 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 :|
