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Subject: Re: [hwloc-users] Patch to disable GCC __builtin_ operations
From: Josh Hursey (jjhursey_at_[hidden])
Date: 2011-06-09 13:27:15


Interesting. Thanks for the tip about the SSE instruction.

In fact one machine has flags of:
------------------
flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov
pat pse36 clflush mmx fxsr sse sse2 ht syscall nx mmxext fxsr_opt
rdtscp lm 3dnowext 3dnow constant_tsc nonstop_tsc pni cx16 popcnt
lahf_lm cmp_legacy svm extapic cr8_legacy altmovcr8 abm sse4a
misalignsse 3dnowprefetch osvw
------------------
While the other only has:
------------------
flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov
pat pse36 clflush mmx fxsr sse sse2 ht syscall nx mmxext fxsr_opt lm
3dnowext 3dnow pni cmp_legacy
------------------

So passing CFLAGS="-mno-sse4a -mno-popcnt" seems to do the trick, and
now I can use the same hwloc on the front and back end nodes.

Thanks for your help. I guess you can disregard the patch then.

Thanks again,
Josh

On Thu, Jun 9, 2011 at 11:18 AM, Samuel Thibault
<samuel.thibault_at_[hidden]> wrote:
> Hello,
>
> Josh Hursey, le Thu 09 Jun 2011 17:03:29 +0200, a écrit :
>> Program terminated with signal 4, Illegal instruction.
>> #0  0x000000000041d8d9 in hwloc_weight_long ()
>
>> 0x000000000041d8d9 <hwloc_weight_long+8>:     popcnt 0xfffffffffffffff8(%rbp),%rax
>
> This is SSE4 indeed.  You could check in grep sse4 /proc/cpuinfo that the frontend
> has it while the computation nodes don't.
>
> Gcc does not emit such instruction unless being instructed to (and
> hwloc does not). Since it does on your machine, there must be something
> on your frontend toolchain which forces -march=native or -march=sse4,
> and you will have other appearances of such bugs, where gcc adds
> SSE4-specific instructions with will SIGILL on the computation nodes,
> and it's probably only by luck that you have not encountered it yet.
>
> Samuel
> _______________________________________________
> hwloc-users mailing list
> hwloc-users_at_[hidden]
> http://www.open-mpi.org/mailman/listinfo.cgi/hwloc-users
>
>

-- 
Joshua Hursey
Postdoctoral Research Associate
Oak Ridge National Laboratory
http://users.nccs.gov/~jjhursey