CPUINFO

[Petros Koutoupis]

I am running on a Dual-Proc Server (2.4 GHz P4 Xeon(s)) and when I run the following command 'cat /proc/cpuinfo' it lists my processors on the command line. My question is, when I have two, why would it list four....does a Linux host see a hyper-threaded processor as two separate? I just find it a little odd that Processor 0 and 1 have the same physical ID of 0 and Processor 2 and 3 have the same physical ID of 3. Anybody else have an explanation to this?

[root@holley mnt]# cat /proc/cpuinfo
processor : 0
vendor_id : GenuineIntel
cpu family : 15
model : 2
model name : Intel(R) Xeon(TM) CPU 2.40GHz
stepping : 9
cpu MHz : 2400.627
cache size : 512 KB
physical id : 0
siblings : 2
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 mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe cid xtpr
bogomips : 4734.97

processor : 1
vendor_id : GenuineIntel
cpu family : 15
model : 2
model name : Intel(R) Xeon(TM) CPU 2.40GHz
stepping : 9
cpu MHz : 2400.627
cache size : 512 KB
physical id : 0
siblings : 2
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 mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe cid xtpr
bogomips : 4784.12

processor : 2
vendor_id : GenuineIntel
cpu family : 15
model : 2
model name : Intel(R) Xeon(TM) CPU 2.40GHz
stepping : 9
cpu MHz : 2400.627
cache size : 512 KB
physical id : 3
siblings : 2
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 mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe cid xtpr
bogomips : 4784.12

processor : 3
vendor_id : GenuineIntel
cpu family : 15
model : 2
model name : Intel(R) Xeon(TM) CPU 2.40GHz
stepping : 9
cpu MHz : 2400.627
cache size : 512 KB
physical id : 3
siblings : 2
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 mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe cid xtpr
bogomips : 4784.12

[Stefann]

I am running on a Dual-Proc Server (2.4 GHz P4 Xeon(s)) and when I run the following command 'cat /proc/cpuinfo' it lists my processors on the command line. My question is, when I have two, why would it list four....does a Linux host see a hyper-threaded processor as two separate? I just find it a little odd that Processor 0 and 1 have the same physical ID of 0 and Processor 2 and 3 have the same physical ID of 3. Anybody else have an explanation to this?

[root@holley mnt]# cat /proc/cpuinfo
processor : 0
vendor_id : GenuineIntel
cpu family : 15
model : 2
model name : Intel(R) Xeon(TM) CPU 2.40GHz
stepping : 9
cpu MHz : 2400.627
cache size : 512 KB
physical id : 0
siblings : 2
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 mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe cid xtpr
bogomips : 4734.97

processor : 1
vendor_id : GenuineIntel
cpu family : 15
model : 2
model name : Intel(R) Xeon(TM) CPU 2.40GHz
stepping : 9
cpu MHz : 2400.627
cache size : 512 KB
physical id : 0
siblings : 2
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 mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe cid xtpr
bogomips : 4784.12

processor : 2
vendor_id : GenuineIntel
cpu family : 15
model : 2
model name : Intel(R) Xeon(TM) CPU 2.40GHz
stepping : 9
cpu MHz : 2400.627
cache size : 512 KB
physical id : 3
siblings : 2
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 mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe cid xtpr
bogomips : 4784.12

processor : 3
vendor_id : GenuineIntel
cpu family : 15
model : 2
model name : Intel(R) Xeon(TM) CPU 2.40GHz
stepping : 9
cpu MHz : 2400.627
cache size : 512 KB
physical id : 3
siblings : 2
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 mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe cid xtpr
bogomips : 4784.12

Yes, HT CPU's are seen as two seperate ones. SMP works by sending on thread to each CPU, as HT allows two threads to be run in one core, it must be seen as two. So two P4-HT's = 4 P4's.

[Petros Koutoupis]

I thought so...thank you very much!

[kosaraju]

We have a system with Intel Dual-core, hyperthreaded cpus. It has a total of 4 cores and /proc/cpuinfo shows the siblings to be 4. We also have another server with the same specs except has total of 8 cores. The siblings is set to 2 in this case. Any ideas why? The 8 core server is using redhat 2.6.9-34.ELlargesmp kernel whereas teh 4 core is running 2.6.9-34 Elsmp kernel.

Any ideas?

Thanks
- Ravi

[kosaraju]

We have a system with Intel Dual-core, hyperthreaded cpus. It has a total of 4 cores and /proc/cpuinfo shows the siblings to be 4. We also have another server with the same specs except has total of 8 cores. The siblings is set to 2 in this case. Any ideas why? The 8 core server is using redhat 2.6.9-34.ELlargesmp kernel whereas teh 4 core is running 2.6.9-34 Elsmp kernel.

Any ideas?

Thanks
- Ravi

Actually, we figured it out (based on another post: http://kerneltrap.org/node/6284), looks like the kernel has acpi switch to disabled. In the grub.conf, after setting acpi=ht, the system comes up with 4 siblings in /proc/cpuinfo.