On Tue, 14 Apr 2020 13:27:34 -0000 Philipp Eppelt <1871...@bugs.launchpad.net> wrote:
> Hi, > > I have to clarify some things mentioned in my last post: > > I only tested the change with an emulated EPYC-v2 CPU, I cannot test on > a physical EPYC CPU at the moment. However, I doubt that the results > will be different regarding the 0x8000_0008.ECX result. > > The topology information printed is from the EPYC-v2 CPU model. I try to > get access to the machine and have a look if -cpu host affects this > topology. > > So there is still the open question for the -enable-kvm -cpu host -smp 4 > case. Shouldn't in this case the topology of the host CPU be reported? topology was never affected by the choice of -cpu, it's up to users to define it using -smp the way they prefer. > In all emulated-CPU cases it's on the user to define the topology or to > live with the generated one (although I think preferring multi-socket > systems is outdated, but it's likely just the case in my 'world'). > > > Cheers, > Philipp > > > On 4/14/20 10:24 AM, Philipp Eppelt wrote: > > Hi, > > > > thanks for looking into this so quickly. > > > > With this patch applied ontop of git commit > > f3bac27cc1e303e1860cc55b9b6889ba39dee587 I still have the issue and it > > reports the same numbers. I like the new usage of the ApicIdSize field. > > > > > > I looked into the mentioned pc_smp_parse() and had it print the topology > > for -smp 4: > > > > qemu-system-x86_64: warning: cpu topology: sockets (4) , dies (1) , > > cores (1) , threads (1) , maxcpus (4), cpus (4) > > > > and with -smp 4,cores=4: > > > > qemu-system-x86_64: warning: cpu topology: sockets (1) , dies (1) , > > cores (4) , threads (1) , maxcpus (4), cpus (4) > > > > As far as I understand it, these are the numbers the cpuid:8000'0008 > > code relies on: > > `cs->nr_cores`, `cs->nr_threads` with `cs` being of type CPUState. > > > > So I think the issue is rooted with the preferring sockets over cores > > when the -smp cmdline option is parsed, as stated in hw/i386/pc.c:729. > > > > I guess this is the same code for Intel and AMD CPUs alike and this > > issue just didn't surface for us on Intel CPUs, as they don't have this > > CPUID leaf and we don't look at the topology. > > > > This seems to boil down to a more careful use of the -smp option on my end. > > > > Thanks again for looking into this. > > > > Cheers, > > Philipp > > > > > > > > On 4/10/20 2:12 AM, Babu Moger wrote: > >> Philipp, > >> Can you please check if this patch works for you. > >> > >> diff --git a/target/i386/cpu.c b/target/i386/cpu.c > >> index 90ffc5f..e467fee 100644 > >> --- a/target/i386/cpu.c > >> +++ b/target/i386/cpu.c > >> @@ -5831,10 +5831,17 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t > >> index, uint32_t count, > >> } > >> *ebx = env->features[FEAT_8000_0008_EBX]; > >> *ecx = 0; > >> - *edx = 0; > >> if (cs->nr_cores * cs->nr_threads > 1) { > >> - *ecx |= (cs->nr_cores * cs->nr_threads) - 1; > >> + unsigned long max_apicids, bits_required; > >> + > >> + max_apicids = (cs->nr_cores * cs->nr_threads) - 1; > >> + if (max_apicids) { > >> + /* Find out the number of bits to represent all the > >> apicids */ > >> + bits_required = find_last_bit(&max_apicids, > >> BITS_PER_BYTE) + 1; > >> + *ecx |= bits_required << 12 | max_apicids; > >> + } > >> } > >> + *edx = 0; > >> break; > >> case 0x8000000A: > >> if (env->features[FEAT_8000_0001_ECX] & CPUID_EXT3_SVM) { > >> > >> > >> On 4/9/20 9:00 AM, Igor Mammedov wrote: > >>> On Thu, 09 Apr 2020 12:58:11 -0000 > >>> Philipp Eppelt <1871...@bugs.launchpad.net> wrote: > >>> > >>>> Public bug reported: > >>>> > >>>> Setup: > >>>> CPU: AMD EPYC-v2 or host's EPYC cpu > >>>> Linux 64-bit fedora host; Kernel version 5.5.15-200.fc31 > >>>> qemu version: self build > >>>> git-head: f3bac27cc1e303e1860cc55b9b6889ba39dee587 > >>>> config: Configured with: '../configure' > >>>> '--target-list=x86_64-softmmu,mips64el-softmmu,mips64-softmmu,mipsel-softmmu,mips-softmmu,i386-softmmu,aarch64-softmmu,arm-softmmu' > >>>> '--prefix=/opt/qemu-master' > >>>> > >>>> Cmdline: > >>>> qemu-system-x86_64 -kernel > >>>> /home/peppelt/code/l4/internal/.build-x86_64/bin/amd64_gen/bootstrap > >>>> -append "" -initrd "./fiasco/.build-x86_64/fiasco , ... " -serial stdio > >>>> -nographic -monitor none -nographic -monitor none -cpu EPYC-v2 -m 4G > >>>> -smp 4 > >>>> > >>>> Issue: > >>>> We are developing an microkernel operating system called L4Re. We > >>>> recently got an AMD EPYC server for testing and we couldn't execute SMP > >>>> tests of our system when running Linux + qemu + VM w/ L4Re. > >>>> In fact, the kernel did not recognize any APs at all. On AMD CPUs the > >>>> kernel checks for the number of cores reported in CPUID leaf > >>>> 0x8000_0008.ECX[NC] or [ApicIdSize]. [0][1] > >>>> > >>>> The physical machine reports for leaf 0x8000_0008: EAX: 0x3030 EBX: > >>>> 0x18cf757 ECX: 0x703f EDX: 0x1000 > >>>> The lower four bits of ECX are the [NC] field and all set. > >>>> > >>>> When querying inside qemu with -enable-kvm -cpu host -smp 4 (basically > >>>> as replacement and addition to the above cmdline) the CPUID leaf shows: > >>>> EAX: 0x3024, EBX: 0x1001000, ECX: 0x0, EDX: 0x0 > >>>> Note, ECX is zero. Indicating that this is no SMP capabale CPU. > >>>> > >>>> I'm debugging it using my local machine and the QEMU provided EPYC-v2 > >>>> CPU model and it is reproducible there as well and reports: EAX: > >>>> 0x3028, EBX: 0x0, ECX: 0x0, EDX: 0x0 > >>>> > >>>> I checked other AMD based CPU models (phenom, opteron_g3/g5) and they > >>>> behave the same. [2] shows the CPUID 0x8000'0008 handling in the QEMU > >>>> source. > >>>> I believe that behavior here is wrong as ECX[NC] should report the > >>>> number of cores per processor, as stated in the AMD manual [2] p.584. In > >>>> my understanding -smp 4 should then lead to ECX[NC] = 0x3. > >>>> > >>>> The following table shows my findings with the -smp option: > >>>> Option | Qemu guest observed ECX value > >>>> -smp 4 | 0x0 > >>>> -smp 4,cores=4 | 0x3 > >>>> -smp 4,cores=2,thread=2 | 0x3 > >>>> -smp 4,cores=4,threads=2 | QEMU boot error: topology false. > >>>> > >>>> Now, I'm asking myself how the terminology of the AMD manual maps to > >>>> QEMU's -smp option. > >>>> Obviously, nr_cores and nr_threads correspond to the cores and threads > >>>> options on the cmdline and cores * threads <= 4 (in this example), but > >>>> what corresponds the X in -smp X to? > >>> I'd say X corresponds to number of logical CPUs. > >>> Depending on presence of other options these are distributed among them > >>> in magical manner > >>> (see pc_smp_parse() for starters) > >>> > >>>> Querying 0x8000'0008 on the physical processor results in different > >>>> reports than quering QEMU's model as does it with -enable-kvm -cpu host. > >>>> > >>>> Furthermore, the ACPI.MADT shows 4 local APICs to be present while the > >>>> CPU leave reports a single core processor. > >>> it matches -smp X as it should be. > >>> > >>>> > >>>> This leads me to the conclusion that CPUID 0x8000'0008.ECX reports the > >>>> wrong number. > >>> CCed author of recent epyc patches who might know how AMD should work > >>> better than me. > >>> > >>>> > >>>> Please let me know, if you need more information from my side. > >>>> > >>>> > >>>> [0] > >>>> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fkernkonzept%2Ffiasco%2Fblob%2F522ccc5f29ab120213cf02d71328e2b879cbbd19%2Fsrc%2Fkern%2Fia32%2Fkernel_thread-ia32.cpp%23L109&data=02%7C01%7Cbabu.moger%40amd.com%7C57569f7959744399655b08d7dc8e6e24%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637220379083511672&sdata=hcFJzLAVQoIh5IN9CP%2F9cUQNOZoBnpRA6FliJur1wzQ%3D&reserved=0 > >>>> [1] > >>>> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fkernkonzept%2Ffiasco%2Fblob%2F522ccc5f29ab120213cf02d71328e2b879cbbd19%2Fsrc%2Fkern%2Fia32%2Fcpu-ia32.cpp%23L1120&data=02%7C01%7Cbabu.moger%40amd.com%7C57569f7959744399655b08d7dc8e6e24%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637220379083511672&sdata=ANJIbYKbwfq2bDelH%2FRLKnDPIUZc1BwxHspmgxLU7gs%3D&reserved=0 > >>>> [2] > >>>> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fqemu%2Fqemu%2Fblob%2Ff2a8261110c32c4dccd84e774d8dd7a0524e00fb%2Ftarget%2Fi386%2Fcpu.c%23L5835&data=02%7C01%7Cbabu.moger%40amd.com%7C57569f7959744399655b08d7dc8e6e24%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637220379083511672&sdata=oj3mv9e5YOzUsfUjXK44gC8LybyWgMKo8JBIrRR%2BmDA%3D&reserved=0 > >>>> [3] > >>>> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.amd.com%2Fsystem%2Ffiles%2FTechDocs%2F24594.pdf&data=02%7C01%7Cbabu.moger%40amd.com%7C57569f7959744399655b08d7dc8e6e24%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637220379083511672&sdata=7Yr3J9ihlqSqXCXKN5JJNTByO3NGI%2BGMz2EqBF2Y4hw%3D&reserved=0 > >>>> > >>>> ** Affects: qemu > >>>> Importance: Undecided > >>>> Status: New > >>>> > >>> > >> > > >