[Beowulf] Threaded code

[Robert G. Brown]

On Mon, 16 Aug 2004, Art Edwards wrote:

> Newbie question:
> 
> We just purchased a dual opteron box that is running an SMP kernel. We
> have built a fortran code using g77 and a pthreaded atlas. Currently, we
> see only one processor. What really simple thing have we missed?

What do you mean you only "see" one processor?  You SHOULD see e.g.:

rgb at ganesh|B:1023>s00 cat /proc/cpuinfo
processor       : 0
vendor_id       : AuthenticAMD
cpu family      : 15
model           : 5
model name      : AMD Opteron(tm) Processor 242
stepping        : 1
cpu MHz         : 1603.699
cache size      : 1024 KB
fpu             : yes
fpu_exception   : yes
cpuid level     : 1
wp              : yes
flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov
pat pse36 clflush mmx fxsr s
e sse2 syscall nx mmxext lm 3dnowext 3dnow
bogomips        : 3153.92
TLB size        : 1088 4K pages
clflush size    : 64
cache_alignment : 64
address sizes   : 40 bits physical, 48 bits virtual
power management: ts ttp

processor       : 1
vendor_id       : AuthenticAMD
cpu family      : 15
model           : 5
model name      : AMD Opteron(tm) Processor 242
stepping        : 1
cpu MHz         : 1603.699
cache size      : 1024 KB
fpu             : yes
fpu_exception   : yes
cpuid level     : 1
wp              : yes
flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov
pat pse36 clflush mmx fxsr s
e sse2 syscall nx mmxext lm 3dnowext 3dnow
bogomips        : 3203.07
TLB size        : 1088 4K pages
clflush size    : 64
cache_alignment : 64
address sizes   : 40 bits physical, 48 bits virtual
power management: ts ttp

If you don't, there are really only two possibilities I can think of.

  a) You aren't really running an SMP kernel, or your SMP kernel is
badly broken.  Check:

rgb at ganesh|B:1024>s00 uname -a
Linux s00 2.6.5-1.358smp #1 SMP Sat May 8 09:28:14 EDT 2004 x86_64 x86_64 x86_64 GNU/Linux

Not a certain check -- depends on how your kernel was labelled more than
on whether or not it really is SMP.  To be double sure, check your
distribution and kernel RPM(s).  This one is from FC2, for example.  If
you're building your own kernels, be certain that you have configured
the kernel for SMP (or consider NOT building your own and instead use
the smp kernel(s) from a reliable x86_64 distro).  Note that the
installation kernel (the one used to actually run a distribution
install) is never an SMP kernel, in case you are somehow still running
that via a PXE/diskless boot.

  b) You don't really have two functioning processors in the box.
Opening the box and physically verifying that there are two CPUs is
called for.  Seriously.  I had this same problem with the very first SMP
system I ever ordered (dual PPros, kernel 2.0.0).  Turned out that the
systems had dual motherboards with only a single CPU mounted -- the
vendor had screwed up the order.  Alternatively you could have two cpus
physically present but CPU2 could be DOA.  Conceivably you could have
two functioning CPUs but a BIOS problem (I don't know if this is
possible on the opteron hardware but it is not IMpossible overall).

Hope this helps,

   rgb

> 
> Art Edwards
> 
> 

-- 
Robert G. Brown	                       http://www.phy.duke.edu/~rgb/
Duke University Dept. of Physics, Box 90305
Durham, N.C. 27708-0305
Phone: 1-919-660-2567  Fax: 919-660-2525     email:rgb at phy.duke.edu