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Thu, 27 Aug 2020 20:21:13 +0000 (UTC) Date: Thu, 27 Aug 2020 22:21:10 +0200 From: Igor Mammedov To: Babu Moger Subject: Re: [PATCH v5 0/8] Remove EPYC mode apicid decode and use generic decode Message-ID: <20200827222110.1c2ee236@imammedo-mac> In-Reply-To: <11489e5f-2285-ddb4-9c35-c9f522d603a0@amd.com> References: <159804762216.39954.15502128500494116468.stgit@naples-babu.amd.com> <20200826143849.59f6970b@redhat.com> <20200826125059.GN168515@redhat.com> <20200826153034.115126cb@redhat.com> <5c00dac9-5ea5-405c-93be-1ac903ddff62@amd.com> <20200826183331.GA3977@work-vm> <11489e5f-2285-ddb4-9c35-c9f522d603a0@amd.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=imammedo@redhat.com X-Mimecast-Spam-Score: 0.002 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Received-SPF: pass client-ip=207.211.31.120; envelope-from=imammedo@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/08/27 02:56:52 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.959, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "Daniel P. =?UTF-8?Q?B?= =?UTF-8?Q?errang=C3=A9?=" , "ehabkost@redhat.com" , "mst@redhat.com" , Michal Privoznik , "qemu-devel@nongnu.org" , "Dr. David Alan Gilbert" , "pbonzini@redhat.com" , "rth@twiddle.net" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, 26 Aug 2020 13:45:51 -0500 Babu Moger wrote: >=20 >=20 > > -----Original Message----- > > From: Dr. David Alan Gilbert > > Sent: Wednesday, August 26, 2020 1:34 PM > > To: Moger, Babu > > Cc: Igor Mammedov ; Daniel P. Berrang=C3=A9 > > ; ehabkost@redhat.com; mst@redhat.com; Michal > > Privoznik ; qemu-devel@nongnu.org; > > pbonzini@redhat.com; rth@twiddle.net > > Subject: Re: [PATCH v5 0/8] Remove EPYC mode apicid decode and use gene= ric > > decode > >=20 > > * Babu Moger (babu.moger@amd.com) wrote: > > > > > > > -----Original Message----- > > > > From: Igor Mammedov > > > > Sent: Wednesday, August 26, 2020 8:31 AM > > > > To: Daniel P. Berrang=C3=83=C2=A9 > > > > Cc: Moger, Babu ; pbonzini@redhat.com; > > > > rth@twiddle.net; ehabkost@redhat.com; qemu-devel@nongnu.org; > > > > mst@redhat.com; Michal Privoznik > > > > 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. Berrang=C3=83=C2=A9 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 > > > > > > 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=3Dhttps%3= A%2 > > > > > > > F%2F > > > > > > > lore.kernel.org%2Fqemu-devel%2Fc0bcc1a6-1d84-a6e7-e468- > > > > d5b437c1b25 > > > > > > > > > > > > > 4%40amd.com%2F&data=3D02%7C01%7Cbabu.moger%40amd.com%7C8a5c > > > > 52f92 > > > > > > > > > > > > > 3f04082a40808d849c43d49%7C3dd8961fe4884e608e11a82d994e183d%7C0%7 > > > > C0 > > > > > > > > > > > > > %7C637340454473508873&sdata=3DVnW28H1v4XwK3GaNGFxu%2BhwiMeA > > > > YO%2B > > > > > > > 3WAzo3DeY5Ha8%3D&reserved=3D0 > > > > > > > > > > > > > > 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. > >=20 > > Indeed on real hardware, I don't think we always see NUMA; my single so= cket, > > 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? >=20 > 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=3Dtrue > 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=3Dtr= ue", 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. =20 (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 pr= oduce unique id. Same, add a warning that there are more than 1 dies but numa is not ena= bled, suggest to enable numa. With current code it produces invalid APIC ID for valid '-smp' combinat= ion, 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 =3D=3D ms->numa_state->num_nodes and make sure that CPUID_Fn8000001E_ECX consistent with cpu mapping provided with "-numa cpu=3D" option. Warnings won't help a lot, but at least they will point out at possible problem when someone complains. > >=20 > > Dave > >=20 > > > > > > patch on top of this series to enfoce that, i.e: > > > > > > > > > > > > if (epyc && !numa) > > > > > > error("EPYC cpu requires numa to be configured") > > > > > > > > > > Please no. This will break 90% of current usage of the EPYC CPU i= n > > > > > real world QEMU deployments. That is way too user hostile to > > > > > introduce as a requirement. > > > > > > > > > > Why do we need to force this ? People have been successfuly usin= g > > > > > EPYC CPUs without NUMA in QEMU for years now. > > > > > > > > > > It might not match behaviour of bare metal silicon, but that > > > > > hasn't obviously caused the world to come crashing down. > > > > So far it produces warning in linux kernel (RHBZ1728166), (resultin= g > > > > performance might be suboptimal), but I haven't seen anyone reporti= ng > > crashes yet. > > > > > > > > > > > > What other options do we have? > > > > Perhaps we can turn on strict check for new machine types only, so > > > > old configs can keep broken topology (CPUID), while new ones would > > > > require -numa and produce correct topology. > > > > > > > > > > > > > > > > > > Regards, > > > > > Daniel > > > > > > > > -- > > Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK >=20