On Tue, Jan 06, 2026 at 02:44:18AM +0000, H. Hartzer wrote: > Hi bugs@, > > 7.8 amd64 incorrectly identifies a Opteron 4256EE as threaded. Thinking > it has 4 cores with 8 threads total. This processor should have 8 > native cores. Thus, 4 cores are disabled unless sysctl hw.smt=1. > > Interestingly, 7.8 correctly identifies the 4162 EE as having 6 native > cores. > > Thank you! > > -Henrich >
According to a quick google search, these CPUs expose their topology (right or wrong) as SMT based on AMD's "CMT" (See cut-paste below). We use the CPU's own reported topology as reported by CPUID when making the decision if something is SMT or not. HTH. -ml ------ The appearance of SMT (Simultaneous Multithreading) in the CPUID topology for an AMD Opteron 4256 EE is a result of the Bulldozer architecture (Valencia) design and how operating systems interpret its CMT (Clustered Multi-Thread) structure. Why SMT is Reported: Module-Based Architecture: The Opteron 4256 EE is built on 4 Bulldozer modules, each containing two integer cores that share certain components, such as the L2 cache and FPU. CPUID Interpretation: To ensure compatibility with Windows and Linux schedulers, AMD processors of this era often export a topology that mimics SMT. The OS sees two "logical cores" per module; because they share resources, the system reports this relationship as a thread-level (SMT) grouping rather than independent physical cores. > dmesg: > > OpenBSD 7.8 (GENERIC.MP) #1: Sat Nov 29 11:02:59 MST 2025 > > [email protected]:/usr/src/sys/arch/amd64/compile/GENERIC.MP > real mem = 34324676608 (32734MB) > avail mem = 33257316352 (31716MB) > random: good seed from bootblocks > mpath0 at root > scsibus0 at mpath0: 256 targets > mainbus0 at root > bios0 at mainbus0: SMBIOS rev. 2.6 @ 0x9ac00 (30 entries) > bios0: vendor American Megatrends Inc. version "3.5" date 01/12/2015 > bios0: Supermicro H8SCM > acpi0 at bios0: ACPI 3.0 > acpi0: sleep states S0 S1 S4 S5 > acpi0: tables DSDT FACP APIC MCFG OEMB HPET SRAT SSDT EINJ BERT ERST HEST > acpi0: wakeup devices PC02(S4) PC03(S4) PC04(S4) PC05(S4) PC06(S4) PC07(S4) > PC09(S4) PC0A(S4) PC0B(S4) PC0C(S4) SBAZ(S4) P0PC(S4) UHC1(S4) UHC2(S4) > UHC3(S4) USB4(S4) [...] > acpitimer0 at acpi0: 3579545 Hz, 24 bits > acpimadt0 at acpi0 addr 0xfee00000: PC-AT compat > cpu0 at mainbus0: apid 16 (boot processor) > cpu0: AMD Opteron(tm) Processor 4256 EE, 1600.68 MHz, 15-01-02, patch 0600063e > cpu0: cpuid 1 > edx=178bfbff<FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,APIC,SEP,MTRR,PGE,MCA,CMOV,PAT,PSE36,CFLUSH,MMX,FXSR,SSE,SSE2,HTT> > ecx=1698220b<SSE3,PCLMUL,MWAIT,SSSE3,CX16,SSE4.1,SSE4.2,POPCNT,AES,XSAVE,AVX> > cpu0: cpuid 6 eax=4<ARAT> ecx=1<EFFFREQ> > cpu0: cpuid 80000001 edx=2fd3fbff<NXE,MMXX,FFXSR,PAGE1GB,RDTSCP,LONG> > ecx=1c93fff<LAHF,CMPLEG,SVM,EAPICSP,AMCR8,ABM,SSE4A,MASSE,3DNOWP,OSVW,IBS,XOP,SKINIT,FMA4,NODEID,TOPEXT,CPCTR> > cpu0: cpuid 80000007 edx=3d9<HWPSTATE,ITSC> > cpu0: cpuid 80000008 ebx=1000<IBPB> > cpu0: 16KB 64b/line 4-way D-cache, 64KB 64b/line 2-way I-cache, 2MB 64b/line > 16-way L2 cache, 8MB 64b/line 64-way L3 cache > cpu0: smt 0, core 0, package 0 > mtrr: Pentium Pro MTRR support, 8 var ranges, 88 fixed ranges > cpu0: apic clock running at 200MHz > cpu0: mwait min=64, max=64, IBE > cpu1 at mainbus0: apid 17 (application processor) > cpu1: AMD Opteron(tm) Processor 4256 EE, 1600.77 MHz, 15-01-02, patch 0600063e > cpu1: cpuid 80000001 ecx=+8000<WDT> > cpu1: smt 1, core 0, package 0 > cpu2 at mainbus0: apid 18 (application processor) > cpu2: AMD Opteron(tm) Processor 4256 EE, 1600.77 MHz, 15-01-02, patch 0600063e > cpu2: cpuid 80000001 ecx=-8000<WDT> > cpu2: smt 0, core 1, package 0 > cpu3 at mainbus0: apid 19 (application processor) > cpu3: AMD Opteron(tm) Processor 4256 EE, 1600.93 MHz, 15-01-02, patch 0600063e > cpu3: cpuid 80000001 ecx=+8000<WDT> > cpu3: smt 1, core 1, package 0 > cpu4 at mainbus0: apid 20 (application processor) > cpu4: AMD Opteron(tm) Processor 4256 EE, 1600.83 MHz, 15-01-02, patch 0600063e > cpu4: cpuid 80000001 ecx=-8000<WDT> > cpu4: smt 0, core 2, package 0 > cpu5 at mainbus0: apid 21 (application processor) > cpu5: AMD Opteron(tm) Processor 4256 EE, 1601.26 MHz, 15-01-02, patch 0600063e > cpu5: cpuid 80000001 ecx=+8000<WDT> > cpu5: smt 1, core 2, package 0 > cpu6 at mainbus0: apid 22 (application processor) > cpu6: AMD Opteron(tm) Processor 4256 EE, 1600.90 MHz, 15-01-02, patch 0600063e > cpu6: cpuid 80000001 ecx=-8000<WDT> > cpu6: smt 0, core 3, package 0 > cpu7 at mainbus0: apid 23 (application processor) > cpu7: AMD Opteron(tm) Processor 4256 EE, 1601.52 MHz, 15-01-02, patch 0600063e > cpu7: cpuid 80000001 ecx=+8000<WDT> > cpu7: smt 1, core 3, package 0 > ioapic0 at mainbus0: apid 0 pa 0xfec00000, version 21, 24 pins > ioapic1 at mainbus0: apid 1 pa 0xfec20000, version 21, 32 pins > acpimcfg0 at acpi0 > acpimcfg0: addr 0xe0000000, bus 0-255 > acpihpet0 at acpi0: 14318180 Hz > acpiprt0 at acpi0: bus 0 (PCI0) > acpiprt1 at acpi0: bus -1 (PC02) > acpiprt2 at acpi0: bus -1 (PC03) > acpiprt3 at acpi0: bus -1 (PC04) > acpiprt4 at acpi0: bus 1 (PC09) > acpiprt5 at acpi0: bus 2 (PC0A) > acpiprt6 at acpi0: bus 3 (P0PC) > acpipci0 at acpi0 PCI0 > acpicmos0 at acpi0 > "PNP0303" at acpi0 not configured > com0 at acpi0 UAR1 addr 0x3f8/0x8 irq 4: ns16550a, 16 byte fifo > com0: console > com1 at acpi0 UAR2 addr 0x2f8/0x8 irq 3: ns16550a, 16 byte fifo > acpibtn0 at acpi0: PWRB > acpicpu0 at acpi0: C2(0@100 io@0x815), C1(@1 halt!), PSS > acpicpu1 at acpi0: C2(0@100 io@0x815), C1(@1 halt!), PSS > acpicpu2 at acpi0: C2(0@100 io@0x815), C1(@1 halt!), PSS > acpicpu3 at acpi0: C2(0@100 io@0x815), C1(@1 halt!), PSS > acpicpu4 at acpi0: C2(0@100 io@0x815), C1(@1 halt!), PSS > acpicpu5 at acpi0: C2(0@100 io@0x815), C1(@1 halt!), PSS > acpicpu6 at acpi0: C2(0@100 io@0x815), C1(@1 halt!), PSS > acpicpu7 at acpi0: C2(0@100 io@0x815), C1(@1 halt!), PSS > ipmi at mainbus0 not configured > cpu0: 1600 MHz: speeds: 1600 1500 1400 1300 1000 MHz > pci0 at mainbus0 bus 0 > pchb0 at pci0 dev 0 function 0 "ATI SR5650 Host" rev 0x02 > ppb0 at pci0 dev 9 function 0 "ATI SR5690 PCIE" rev 0x00: msi > pci1 at ppb0 bus 1 > em0 at pci1 dev 0 function 0 "Intel 82574L" rev 0x00: msi, address > 0c:c4:7a:76:00:7c > ppb1 at pci0 dev 10 function 0 "ATI SR5690 PCIE" rev 0x00: msi > pci2 at ppb1 bus 2 > em1 at pci2 dev 0 function 0 "Intel 82574L" rev 0x00: msi, address > 0c:c4:7a:76:00:7d > ahci0 at pci0 dev 17 function 0 "ATI SBx00 SATA" rev 0x00: apic 0 int 22, > AHCI 1.1 > ahci0: port 0: 3.0Gb/s > scsibus1 at ahci0: 32 targets > sd0 at scsibus1 targ 0 lun 0: <ATA, WDC WD1000DHTZ-0, 04.0> > naa.50014ee65ac669ef > sd0: 953869MB, 512 bytes/sector, 1953525168 sectors > ohci0 at pci0 dev 18 function 0 "ATI SB700 USB" rev 0x00: apic 0 int 16, > version 1.0, legacy support > ohci1 at pci0 dev 18 function 1 "ATI SB700 USB" rev 0x00: apic 0 int 16, > version 1.0, legacy support > ehci0 at pci0 dev 18 function 2 "ATI SB700 USB2" rev 0x00: apic 0 int 17 > usb0 at ehci0: USB revision 2.0 > uhub0 at usb0 configuration 1 interface 0 "ATI EHCI root hub" rev 2.00/1.00 > addr 1 > ohci2 at pci0 dev 19 function 0 "ATI SB700 USB" rev 0x00: apic 0 int 18, > version 1.0, legacy support > ohci3 at pci0 dev 19 function 1 "ATI SB700 USB" rev 0x00: apic 0 int 18, > version 1.0, legacy support > ehci1 at pci0 dev 19 function 2 "ATI SB700 USB2" rev 0x00: apic 0 int 19 > usb1 at ehci1: USB revision 2.0 > uhub1 at usb1 configuration 1 interface 0 "ATI EHCI root hub" rev 2.00/1.00 > addr 1 > piixpm0 at pci0 dev 20 function 0 "ATI SBx00 SMBus" rev 0x3d: SMI > iic0 at piixpm0 > sdtemp0 at iic0 addr 0x18: cat34ts02 > sdtemp1 at iic0 addr 0x19: cat34ts02 > sdtemp2 at iic0 addr 0x1a: cat34ts02 > sdtemp3 at iic0 addr 0x1b: stts2002 > nvt0 at iic0 addr 0x2f: W83795G > spdmem0 at iic0 addr 0x50: 8GB DDR3 SDRAM registered ECC PC3-10600 with > thermal sensor > spdmem1 at iic0 addr 0x51: 8GB DDR3 SDRAM registered ECC PC3-10600 with > thermal sensor > spdmem2 at iic0 addr 0x52: 8GB DDR3 SDRAM registered ECC PC3-10600 with > thermal sensor > spdmem3 at iic0 addr 0x53: 8GB DDR3 SDRAM registered ECC PC3-10600 with > thermal sensor > pcib0 at pci0 dev 20 function 3 "ATI SB700 ISA" rev 0x00 > ppb2 at pci0 dev 20 function 4 "ATI SB600 PCI" rev 0x00 > pci3 at ppb2 bus 3 > vga1 at pci3 dev 4 function 0 "Matrox MGA G200eW" rev 0x0a > wsdisplay at vga1 not configured > ohci4 at pci0 dev 20 function 5 "ATI SB700 USB" rev 0x00: apic 0 int 18, > version 1.0, legacy support > pchb1 at pci0 dev 24 function 0 "AMD 15/0xh Link Cfg" rev 0x00 > pchb2 at pci0 dev 24 function 1 "AMD 15/0xh Address Map" rev 0x00 > pchb3 at pci0 dev 24 function 2 "AMD 15/0xh DRAM Cfg" rev 0x00 > km0 at pci0 dev 24 function 3 "AMD 15/0xh Misc Cfg" rev 0x00 > pchb4 at pci0 dev 24 function 4 "AMD 15/0xh CPU Power" rev 0x00 > pchb5 at pci0 dev 24 function 5 "AMD 15/0xh Host" rev 0x00 > usb2 at ohci0: USB revision 1.0 > uhub2 at usb2 configuration 1 interface 0 "ATI OHCI root hub" rev 1.00/1.00 > addr 1 > usb3 at ohci1: USB revision 1.0 > uhub3 at usb3 configuration 1 interface 0 "ATI OHCI root hub" rev 1.00/1.00 > addr 1 > usb4 at ohci2: USB revision 1.0 > uhub4 at usb4 configuration 1 interface 0 "ATI OHCI root hub" rev 1.00/1.00 > addr 1 > usb5 at ohci3: USB revision 1.0 > uhub5 at usb5 configuration 1 interface 0 "ATI OHCI root hub" rev 1.00/1.00 > addr 1 > isa0 at pcib0 > isadma0 at isa0 > pckbc0 at isa0 port 0x60/5 irq 1 irq 12 > pckbd0 at pckbc0 (kbd slot) > wskbd0 at pckbd0 mux 1 > pcppi0 at isa0 port 0x61 > spkr0 at pcppi0 > wbsio0 at isa0 port 0x2e/2: W83627DHG-P rev 0x73 > wbsio0 port 0xa10/2 not configured > usb6 at ohci4: USB revision 1.0 > uhub6 at usb6 configuration 1 interface 0 "ATI OHCI root hub" rev 1.00/1.00 > addr 1 > vmm0 at mainbus0: SVM/RVI > vscsi0 at root > scsibus2 at vscsi0: 256 targets > softraid0 at root > scsibus3 at softraid0: 256 targets > root on sd0a (8571f49c59f83abb.a) swap on sd0b dump on sd0b >
