[petsc-dev] error with flags PETSc uses for determining AVX

[Barry Smith]

> On Feb 13, 2021, at 11:58 PM, Jed Brown <jed at jedbrown.org> wrote:
> 
> I usually configure --with-debugging=0 COPTFLAGS='-O2 -march=native' or similar. There's a tension here between optimizing aggressively for the current machine and making binaries that work on other machines. Most configure systems default to making somewhat portable binaries, so that's a principal of least surprise. (Though you're no novice and seem to have been surprised anyway.)
> 
> I'd kinda prefer if we recommended making portable binaries that run-time detected when to use newer instructions where it matters.

   How do we do this? What can we put in configure to do this.

   Yes, I never paid attention to the AVX nonsense over the years and never realized that Intel and Gnu (and hence PETSc)  both compile by default for machines I used in my twenties.

   Expecting PETSc users to automatically add -march= is not realistic.  I will try to rig something up in configure where if the user does not provide march something reasonable is selected. 

  Barry


> 
> Barry Smith <bsmith at petsc.dev> writes:
> 
>>  Shouldn't configure be setting something appropriate for this automatically? This is nuts, it means when users do a ./configure make unless they pass weird arguments they sure as heck don't know about to the compiler they won't get any of the glory that they expect and that has been in almost all Intel systems forever.
>> 
>>  Barry
>> 
>>  I run ./configure --with-debugging=0 and I get none of the stuff added by Intel for 15+ years?
>> 
>> 
>>> On Feb 13, 2021, at 11:26 PM, Jed Brown <jed at jedbrown.org> wrote:
>>> 
>>> Use -march=native or similar. The default target is basic x86_64, which has only SSE2.
>>> 
>>> Barry Smith <bsmith at petsc.dev> writes:
>>> 
>>>> PETSc source has code like defined(__AVX2__) in the source but it does not seem to be able to find any of these macros (icc or gcc) on the petsc-02 system
>>>> 
>>>> Are these macros supposed to be defined? How does on get them to be defined? Why are they not define? What am I doing wrong?
>>>> 
>>>> Keep reading
>>>> 
>>>> $ lscpu 
>>>> Architecture:        x86_64
>>>> CPU op-mode(s):      32-bit, 64-bit
>>>> Byte Order:          Little Endian
>>>> CPU(s):              64
>>>> On-line CPU(s) list: 0-63
>>>> Thread(s) per core:  2
>>>> Core(s) per socket:  16
>>>> Socket(s):           2
>>>> NUMA node(s):        2
>>>> Vendor ID:           GenuineIntel
>>>> CPU family:          6
>>>> Model:               85
>>>> Model name:          Intel(R) Xeon(R) Gold 5218 CPU @ 2.30GHz
>>>> Stepping:            7
>>>> CPU MHz:             1000.603
>>>> CPU max MHz:         2301.0000
>>>> CPU min MHz:         1000.0000
>>>> BogoMIPS:            4600.00
>>>> Virtualization:      VT-x
>>>> L1d cache:           32K
>>>> L1i cache:           32K
>>>> L2 cache:            1024K
>>>> L3 cache:            22528K
>>>> NUMA node0 CPU(s):   0-15,32-47
>>>> NUMA node1 CPU(s):   16-31,48-63
>>>> 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 pdpe1gb rdtscp lm constant_tsc art arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc cpuid aperfmperf pni pclmulqdq dtes64 monitor ds_cpl vmx smx est tm2 ssse3 sdbg fma cx16 xtpr pdcm pcid dca sse4_1 sse4_2 x2apic movbe popcnt tsc_deadline_timer aes xsave avx f16c rdrand lahf_lm abm 3dnowprefetch cpuid_fault epb cat_l3 cdp_l3 invpcid_single intel_ppin ssbd mba ibrs ibpb stibp ibrs_enhanced tpr_shadow vnmi flexpriority ept vpid fsgsbase tsc_adjust bmi1 avx2 smep bmi2 erms invpcid cqm mpx rdt_a avx512f avx512dq rdseed adx smap clflushopt clwb intel_pt avx512cd avx512bw avx512vl xsaveopt xsavec xgetbv1 xsaves cqm_llc cqm_occup_llc cqm_mbm_total cqm_mbm_local dtherm ida arat pln pts pku ospke avx512_vnni md_clear flush_l1d arch_capabilities
>>>> 
>>>> Test program 
>>>> 
>>>> #if defined(__FMA__)
>>>> #error FMA
>>>> #endif
>>>> 
>>>> #if defined(__AVX512F__)
>>>> #error AVX512F
>>>> #endif
>>>> 
>>>> #if defined(__AVX2__)
>>>> #error AVX2
>>>> #endif
>>>> 
>>>> 
>>>> icc mytest.c
>>>> /usr/lib/gcc/x86_64-linux-gnu/7/../../../x86_64-linux-gnu/Scrt1.o: In function `_start':
>>>> (.text+0x20): undefined reference to `main'