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List: linux-smp
Subject: AW: Hyper-Threading disabled on Pentium 4
From: "Bernhard Lummer" <b.lummer () highyag ! de>
Date: 2004-08-26 13:27:14
Message-ID: NHBBJBKGNIBPBLKOBGOIMEGOEHAA.b.lummer () highyag ! de
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Hi,
May be this helps?
http://seclists.org/lists/linux-kernel/2002/Dec/3261.html
Good luck!
Bernhard
> -----Ursprüngliche Nachricht-----
> Von: linux-smp-owner@vger.kernel.org
> [mailto:linux-smp-owner@vger.kernel.org]Im Auftrag von Urs Thuermann
> Gesendet: Donnerstag, 26. August 2004 13:17
> An: linux-smp@vger.kernel.org
> 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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>
>
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