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XelKarin
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Joined: 29 Dec 2003
Posts: 41

PostPosted: Thu Dec 14, 2017 5:45 pm    Post subject: Hyperthreading not enabled on Xeon 5140 Reply with quote

I have a fairly old Xeon system that supposedly supports hyperthreading, but Linux is not taking advantage of it. I have CONFIG_SCHED_SMT enabled in the kernel configuration, and I've checked BIOS settings carefully, but couldn't find an option to enable or disable hyperthreading there. Are there any other ways to enable hyperthreading? Is there some reason why the kernel would choose to not use hyperthreading even though the processor supports it?

lscpu
Code:
Architecture:        i686
CPU op-mode(s):      32-bit, 64-bit
Byte Order:          Little Endian
CPU(s):              4
On-line CPU(s) list: 0-3
Thread(s) per core:  1
Core(s) per socket:  2
Socket(s):           2
Vendor ID:           GenuineIntel
CPU family:          6
Model:               15
Model name:          Intel(R) Xeon(R) CPU            5140  @ 2.33GHz
Stepping:            6
CPU MHz:             2333.527
BogoMIPS:            4667.05
Virtualization:      VT-x
L1d cache:           32K
L1i cache:           32K
L2 cache:            4096K
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 nx lm constant_tsc arch_perfmon pebs bts cpuid aperfmperf pni dtes64 monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr pdcm dca lahf_lm tpr_shadow dtherm


/proc/cpuinfo
Code:
processor   : 0
vendor_id   : GenuineIntel
cpu family   : 6
model      : 15
model name   : Intel(R) Xeon(R) CPU            5140  @ 2.33GHz
stepping   : 6
microcode   : 0xcd
cpu MHz      : 2333.527
cache size   : 4096 KB
physical id   : 0
siblings   : 2
core id      : 0
cpu cores   : 2
apicid      : 0
initial apicid   : 0
fdiv_bug   : no
f00f_bug   : no
coma_bug   : no
fpu      : yes
fpu_exception   : yes
cpuid level   : 10
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 nx lm constant_tsc arch_perfmon pebs bts cpuid aperfmperf pni dtes64 monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr pdcm dca lahf_lm tpr_shadow dtherm
bugs      :
bogomips   : 4667.05
clflush size   : 64
cache_alignment   : 64
address sizes   : 36 bits physical, 48 bits virtual
power management:

processor   : 1
vendor_id   : GenuineIntel
cpu family   : 6
model      : 15
model name   : Intel(R) Xeon(R) CPU            5140  @ 2.33GHz
stepping   : 6
microcode   : 0xcd
cpu MHz      : 2333.527
cache size   : 4096 KB
physical id   : 3
siblings   : 2
core id      : 0
cpu cores   : 2
apicid      : 6
initial apicid   : 6
fdiv_bug   : no
f00f_bug   : no
coma_bug   : no
fpu      : yes
fpu_exception   : yes
cpuid level   : 10
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 nx lm constant_tsc arch_perfmon pebs bts cpuid aperfmperf pni dtes64 monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr pdcm dca lahf_lm tpr_shadow dtherm
bugs      :
bogomips   : 4666.75
clflush size   : 64
cache_alignment   : 64
address sizes   : 36 bits physical, 48 bits virtual
power management:

processor   : 2
vendor_id   : GenuineIntel
cpu family   : 6
model      : 15
model name   : Intel(R) Xeon(R) CPU            5140  @ 2.33GHz
stepping   : 6
microcode   : 0xcd
cpu MHz      : 2333.527
cache size   : 4096 KB
physical id   : 0
siblings   : 2
core id      : 1
cpu cores   : 2
apicid      : 1
initial apicid   : 1
fdiv_bug   : no
f00f_bug   : no
coma_bug   : no
fpu      : yes
fpu_exception   : yes
cpuid level   : 10
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 nx lm constant_tsc arch_perfmon pebs bts cpuid aperfmperf pni dtes64 monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr pdcm dca lahf_lm tpr_shadow dtherm
bugs      :
bogomips   : 4666.77
clflush size   : 64
cache_alignment   : 64
address sizes   : 36 bits physical, 48 bits virtual
power management:

processor   : 3
vendor_id   : GenuineIntel
cpu family   : 6
model      : 15
model name   : Intel(R) Xeon(R) CPU            5140  @ 2.33GHz
stepping   : 6
microcode   : 0xcd
cpu MHz      : 2333.527
cache size   : 4096 KB
physical id   : 3
siblings   : 2
core id      : 1
cpu cores   : 2
apicid      : 7
initial apicid   : 7
fdiv_bug   : no
f00f_bug   : no
coma_bug   : no
fpu      : yes
fpu_exception   : yes
cpuid level   : 10
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 nx lm constant_tsc arch_perfmon pebs bts cpuid aperfmperf pni dtes64 monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr pdcm dca lahf_lm tpr_shadow dtherm
bugs      :
bogomips   : 4666.73
clflush size   : 64
cache_alignment   : 64
address sizes   : 36 bits physical, 48 bits virtual
power management:
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eccerr0r
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Joined: 01 Jul 2004
Posts: 7132
Location: almost Mile High in the USA

PostPosted: Thu Dec 14, 2017 9:19 pm    Post subject: Reply with quote

The 5140 is a dual core dual thread, and for Linux a dual core dual thread should show up as 4 processors.

So if you have one cpu plugged into the machine, you see 4 "processors" in /proc/cpuinfo .

If you have two CPUs plugged in... Hyperthreading requires BIOS support and if BIOS can't enable it, it's dead in the water.

The important kernel option is "CONFIG_SMP" which you have enabled. The other ones, including the SMT one, just make the scheduler smarter to deal with the cores/threads.
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mike155
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Joined: 17 Sep 2010
Posts: 1294
Location: Frankfurt, Germany

PostPosted: Thu Dec 14, 2017 9:48 pm    Post subject: Reply with quote

Why do you think that Intel Xeon Processor 5140 supports Hyperthreading?

Look at https://ark.intel.com/products/27217/Intel-Xeon-Processor-5140-4M-Cache-2_33-GHz-1333-MHz-FSB:
Quote:
Intel Hyper-Threading Technology: No
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joanandk
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Joined: 12 Feb 2017
Posts: 80

PostPosted: Thu Dec 14, 2017 10:00 pm    Post subject: Reply with quote

@XelKarin: Don't break your head for hyperthreading. My measurements on mutliple systems show that ht only enhances computational power of 15-25%. So if you have one core with ht it would be max 125% compared to 100% without ht.

So your benefits would be marginal and you would be on a better side if you upgrade your two processors with 4 core cpus.

BR
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eccerr0r
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PostPosted: Fri Dec 15, 2017 12:07 am    Post subject: Reply with quote

Ah it looks like the 5140 may actually be one of the units that has CPUID reporting "ht" but doesn't actually support hyperthreading, similar to my Core2Quad...

The extra 25% is nothing to sneeze at if you can get that much, though I've seen a good 10% or so boost with HT on average . Might not seem much but over large jobs it adds up. Just hope you don't run workloads where it's detrimental (rare.)
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XelKarin
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Joined: 29 Dec 2003
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PostPosted: Fri Dec 15, 2017 11:44 pm    Post subject: Reply with quote

It's actually a system I use for testing, so performance isn't too critical. A little more would have been helpful though. I mainly just noticed that it wasn't making use of hyperthreads even though Linux detects it as having them available. Not just /proc/cpuinfo and lscpu, but dmidecode reports that the system supports hyperthreads as well. I guess Intel's specs are what's correct though. Anyways, thanks for the help everyone.
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