# disabling hyperthreading when no access to bios in freebsd8



## chrcol (Mar 21, 2010)

Hi

on freebsd7 I see the following sysctl.


```
machdep.hlt_logical_cpus
```

on freebsd8 its missing, any ideas? the docs indicate it still should be there and SMP is enabled.

processor is an i7 and hyperthreading is on.


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## gcooper@ (Mar 21, 2010)

The sysctl and kernel tunable are still there, so I think that the logic for determining whether or not a CPU is logical is incorrect for i7 (even on 9-CURRENT). I'll talk to jhb@ about this and see if it can get resolved and MFCed.


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## gcooper@ (Mar 21, 2010)

I've done some more poking around and it appears that it does properly detect that they're logical processors (note SMT):


```
CPU: Intel(R) Xeon(R) CPU           W3520  @ 2.67GHz (2694.12-MHz K8-class CPU)
  Origin = "GenuineIntel"  Id = 0x106a5  Family = 6  Model = 1a  Stepping = 5
  Features=0xbfebfbff<FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,APIC,SEP,MTRR,PGE,MCA,CMOV,PAT,PSE36,CLFLUSH,DTS,ACPI,MMX,FXSR,SSE,SSE2,SS,HTT,TM,PBE>
  Features2=0x9ce3bd<SSE3,DTES64,MON,DS_CPL,VMX,EST,TM2,SSSE3,CX16,xTPR,PDCM,DCA,SSE4.1,SSE4.2,POPCNT>
  AMD Features=0x28100800<SYSCALL,NX,RDTSCP,LM>
  AMD Features2=0x1<LAHF>
  TSC: P-state invariant
real memory  = 12884901888 (12288 MB)
avail memory = 12379992064 (11806 MB)
ACPI APIC Table: <091109 APIC2100>
FreeBSD/SMP: Multiprocessor System Detected: 8 CPUs
FreeBSD/SMP: 1 package(s) x 4 core(s) x 2 SMT threads
 cpu0 (BSP): APIC ID:  0
 cpu1 (AP): APIC ID:  1
 cpu2 (AP): APIC ID:  2
 cpu3 (AP): APIC ID:  3
 cpu4 (AP): APIC ID:  4
 cpu5 (AP): APIC ID:  5
 cpu6 (AP): APIC ID:  6
 cpu7 (AP): APIC ID:  7
```

I'm emailing jhb@ to see if this is a known issue or the implementation was done this way on purpose.


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## chrcol (Mar 23, 2010)

ok thanks for the response.

here is confirmation of the SMT also.


```
CPU: Intel(R) Core(TM) i7 CPU         920  @ 2.67GHz (2684.00-MHz K8-class CPU)
  Origin = "GenuineIntel"  Id = 0x106a5  Stepping = 5
  Features=0xbfebfbff<FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,APIC,SEP,MTRR,PGE,MCA,CMOV,PAT,PSE36,CLFLUSH,DTS,ACPI,MMX,FXSR,SSE,SSE2,SS,HTT,TM,PBE>
  Features2=0x98e3bd<SSE3,DTES64,MON,DS_CPL,VMX,EST,TM2,SSSE3,CX16,xTPR,PDCM,SSE4.1,SSE4.2,POPCNT>
  AMD Features=0x28100800<SYSCALL,NX,RDTSCP,LM>
  AMD Features2=0x1<LAHF>
  TSC: P-state invariant
real memory  = 12889096192 (12292 MB)
avail memory = 12312739840 (11742 MB)
ACPI APIC Table: <7522MS A7522800>
FreeBSD/SMP: Multiprocessor System Detected: 8 CPUs
FreeBSD/SMP: 1 package(s) x 4 core(s) x 2 SMT threads
```


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## gcooper@ (Apr 4, 2010)

Here's the PR I've opened for the issue: http://www.freebsd.org/cgi/query-pr.cgi?pr=145385


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