For MPI hosts file, how many slots

Question

I have 2 computers I am using in a small cluster. Each has 2 Intel Xeon quad-cord processors.

I just wanted to verify that in my host file, I should specify 8 slots per host.

The tail of the /proc/cpu file looks like the following (with procs 0 - 6 before this):

.... processors 0-6 above ....

processor   : 7
vendor_id   : GenuineIntel
cpu family  : 6
model       : 23
model name  : Intel(R) Xeon(R) CPU           E5420  @ 2.50GHz
stepping    : 6
microcode   : 0x606
cpu MHz     : 1998.000
cache size  : 6144 KB
physical id : 1
siblings    : 4
core id     : 3
cpu cores   : 4
apicid      : 7
initial apicid  : 7
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 syscall nx lm constant_tsc arch_perfmon pebs bts rep_good nopl aperfmperf pni dtes64 monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr pdcm dca sse4_1 lahf_lm dtherm tpr_shadow vnmi flexpriority
bogomips    : 4987.49
clflush size    : 64
cache_alignment : 64
address sizes   : 38 bits physical, 48 bits virtual
power management:

Answer 1

8 hosts per node would certainly be a valid way of doing things.

You could potentially also use fewer if you plan to do something like use MPI + threads. It just depends on your application. In general though, it is a safe way to go to say that you plan to use 1 rank per core.