AW: Hyper-Threading disabled on Pentium 4

Hi,
May be this helps?
http://seclists.org/lists/linux-kernel/2002/Dec/3261.html

Good luck!
Bernhard


> -----Ursprüngliche Nachricht-----
> Von: [email protected]
> [mailto:[email protected]]Im Auftrag von Urs Thuermann
> Gesendet: Donnerstag, 26. August 2004 13:17
> An: [email protected]
> Betreff: Hyper-Threading disabled on Pentium 4
>
>
> I'd like to run an SMP kernel with Hyper-Threading on a Pentium 4
> processor, but dmesg tells me, it's disabled.  Sorry, I don't know
> what mainboard this is.
>
> AFAIK, the CPU is able to do Hyper-Threading, and also /proc/cpuinfo
> seems to indicate so:
>
>     $ cat /proc/cpuinfo
>     processor       : 0
>     vendor_id       : GenuineIntel
>     cpu family      : 15
>     model           : 2
>     model name      : Intel(R) Pentium(R) 4 CPU 2.40GHz
>     stepping        : 7
>     cpu MHz         : 2424.718
>     cache size      : 512 KB
>     physical id     : 0
>     siblings        : 1
>     fdiv_bug        : no
>     hlt_bug         : no
>     f00f_bug        : no
>     coma_bug        : no
>     fpu             : yes
>     fpu_exception   : yes
>     cpuid level     : 2
>     wp              : yes
>     flags           : 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
> ht tm pbe cid
>     bogomips        : 4784.12
>
>     $
>
> I think, the ht flag means Hyper-Threading, right?  However, when I
> boot with a Linux-2.6.7 SMP kernel, I find the following in dmesg
> output:
>
>     Initializing CPU#0
>     PID hash table entries: 2048 (order 11: 16384 bytes)
>     Detected 2424.718 MHz processor.
>     Using tsc for high-res timesource
>     Console: colour VGA+ 80x25
>     Memory: 515808k/524208k available (1769k kernel code, 7656k
> reserved, 606k data, 372k init, 0k highmem)
>     Checking if this processor honours the WP bit even in
> supervisor mode... Ok.
>     Calibrating delay loop... 4784.12 BogoMIPS
>     Security Scaffold v1.0.0 initialized
>     Dentry cache hash table entries: 65536 (order: 6, 262144 bytes)
>     Inode-cache hash table entries: 32768 (order: 5, 131072 bytes)
>     Mount-cache hash table entries: 512 (order: 0, 4096 bytes)
>     CPU:     After generic identify, caps: bfebfbff 00000000
> 00000000 00000000
>     CPU:     After vendor identify, caps: bfebfbff 00000000
> 00000000 00000000
>     CPU: Trace cache: 12K uops, L1 D cache: 8K
>     CPU: L2 cache: 512K
>     CPU: Hyper-Threading is disabled
>     CPU:     After all inits, caps: bfebfbff 00000000 00000000 00000080
>     Intel machine check architecture supported.
>     Intel machine check reporting enabled on CPU#0.
>     CPU0: Intel P4/Xeon Extended MCE MSRs (12) available
>     CPU0: Thermal monitoring enabled
>     Enabling fast FPU save and restore... done.
>     Enabling unmasked SIMD FPU exception support... done.
>     Checking 'hlt' instruction... OK.
>     CPU0: Intel(R) Pentium(R) 4 CPU 2.40GHz stepping 07
>     per-CPU timeslice cutoff: 1462.74 usecs.
>
> Looking into linux-2.6.7/arch/i386/kernel/cpu/intel.c, I found the
> message comes from the code
>
>      cpuid(1, &eax, &ebx, &ecx, &edx);
>      smp_num_siblings = (ebx & 0xff0000) >> 16;
>
>      if (smp_num_siblings == 1) {
>              printk(KERN_INFO  "CPU: Hyper-Threading is disabled\n");
>      } else if (smp_num_siblings > 1 ) {
>
> So why does the CPUID instruction yield only one sibling?  Is this a
> known problem?  Is there a way to enable Hyper-Threading on that
> machine?
>
>
> urs
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