[llvm-bugs] [Bug 40727] New: OpenMP runtime detects incorrect processor topology on AMD CPUs

Wed Feb 13 17:07:06 PST 2019

https://bugs.llvm.org/show_bug.cgi?id=40727

            Bug ID: 40727
           Summary: OpenMP runtime detects incorrect processor topology on
                    AMD CPUs
           Product: OpenMP
           Version: unspecified
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Runtime Library
          Assignee: unassignedbugs at nondot.org
          Reporter: steven at uplinklabs.net
                CC: llvm-bugs at lists.llvm.org

The processor topology detection in the OpenMP runtime is confused by AMD CPUs:

$ env KMP_AFFINITY=scatter,verbose ./nbody --bodies 64 --no-crosscheck
--iterations 1 --cycle-after 5
OMP: Info #211: KMP_AFFINITY: decoding x2APIC ids.
OMP: Info #212: KMP_AFFINITY: cpuid leaf 11 not supported - decoding legacy
APIC ids.
OMP: Info #149: KMP_AFFINITY: Affinity capable, using global cpuid info
OMP: Info #154: KMP_AFFINITY: Initial OS proc set respected: 0-15
OMP: Info #156: KMP_AFFINITY: 16 available OS procs
OMP: Info #157: KMP_AFFINITY: Uniform topology
OMP: Info #159: KMP_AFFINITY: 1 packages x 1 cores/pkg x 16 threads/core (1
total cores)
OMP: Info #213: KMP_AFFINITY: OS proc to physical thread map:
OMP: Info #171: KMP_AFFINITY: OS proc 0 maps to package 0 thread 0 
OMP: Info #171: KMP_AFFINITY: OS proc 1 maps to package 0 thread 1 
OMP: Info #171: KMP_AFFINITY: OS proc 2 maps to package 0 thread 2 
OMP: Info #171: KMP_AFFINITY: OS proc 3 maps to package 0 thread 3 
OMP: Info #171: KMP_AFFINITY: OS proc 4 maps to package 0 thread 4 
OMP: Info #171: KMP_AFFINITY: OS proc 5 maps to package 0 thread 5 
OMP: Info #171: KMP_AFFINITY: OS proc 6 maps to package 0 thread 6 
OMP: Info #171: KMP_AFFINITY: OS proc 7 maps to package 0 thread 7 
OMP: Info #171: KMP_AFFINITY: OS proc 8 maps to package 0 thread 8 
OMP: Info #171: KMP_AFFINITY: OS proc 9 maps to package 0 thread 9 
OMP: Info #171: KMP_AFFINITY: OS proc 10 maps to package 0 thread 10 
OMP: Info #171: KMP_AFFINITY: OS proc 11 maps to package 0 thread 11 
OMP: Info #171: KMP_AFFINITY: OS proc 12 maps to package 0 thread 12 
OMP: Info #171: KMP_AFFINITY: OS proc 13 maps to package 0 thread 13 
OMP: Info #171: KMP_AFFINITY: OS proc 14 maps to package 0 thread 14 
OMP: Info #171: KMP_AFFINITY: OS proc 15 maps to package 0 thread 15 
OMP: Info #144: KMP_AFFINITY: Threads may migrate across 1 innermost levels of
machine
OMP: Info #249: KMP_AFFINITY: pid 7608 tid 7608 thread 0 bound to OS proc set
0-15
OMP: Info #249: KMP_AFFINITY: pid 7608 tid 7610 thread 1 bound to OS proc set
0-15
OMP: Info #249: KMP_AFFINITY: pid 7608 tid 7611 thread 2 bound to OS proc set
0-15
OMP: Info #249: KMP_AFFINITY: pid 7608 tid 7612 thread 3 bound to OS proc set
0-15
OMP: Info #249: KMP_AFFINITY: pid 7608 tid 7613 thread 4 bound to OS proc set
0-15
OMP: Info #249: KMP_AFFINITY: pid 7608 tid 7614 thread 5 bound to OS proc set
0-15
OMP: Info #249: KMP_AFFINITY: pid 7608 tid 7615 thread 6 bound to OS proc set
0-15
OMP: Info #249: KMP_AFFINITY: pid 7608 tid 7616 thread 7 bound to OS proc set
0-15
OMP: Info #249: KMP_AFFINITY: pid 7608 tid 7617 thread 8 bound to OS proc set
0-15
OMP: Info #249: KMP_AFFINITY: pid 7608 tid 7618 thread 9 bound to OS proc set
0-15
OMP: Info #249: KMP_AFFINITY: pid 7608 tid 7619 thread 10 bound to OS proc set
0-15
OMP: Info #249: KMP_AFFINITY: pid 7608 tid 7620 thread 11 bound to OS proc set
0-15
OMP: Info #249: KMP_AFFINITY: pid 7608 tid 7621 thread 12 bound to OS proc set
0-15
OMP: Info #249: KMP_AFFINITY: pid 7608 tid 7622 thread 13 bound to OS proc set
0-15
OMP: Info #249: KMP_AFFINITY: pid 7608 tid 7623 thread 14 bound to OS proc set
0-15
OMP: Info #249: KMP_AFFINITY: pid 7608 tid 7624 thread 15 bound to OS proc set
0-15

$ lscpu
Architecture:        x86_64
CPU op-mode(s):      32-bit, 64-bit
Byte Order:          Little Endian
Address sizes:       43 bits physical, 48 bits virtual
CPU(s):              16
On-line CPU(s) list: 0-15
Thread(s) per core:  2
Core(s) per socket:  8
Socket(s):           1
NUMA node(s):        1
Vendor ID:           AuthenticAMD
CPU family:          23
Model:               8
Model name:          AMD Ryzen 7 2700X Eight-Core Processor
Stepping:            2
CPU MHz:             4200.705
CPU max MHz:         3700.0000
CPU min MHz:         2200.0000
BogoMIPS:            7384.85
Virtualization:      AMD-V
L1d cache:           32K
L1i cache:           64K
L2 cache:            512K
L3 cache:            8192K
NUMA node0 CPU(s):   0-15
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 pdpe1gb
rdtscp lm constant_tsc rep_good nopl nonstop_tsc cpuid extd_apicid aperfmperf
pni pclmulqdq monitor ssse3 fma cx16 sse4_1 sse4_2 movbe popcnt aes xsave avx
f16c rdrand lahf_lm cmp_legacy svm extapic cr8_legacy abm sse4a misalignsse
3dnowprefetch osvw skinit wdt tce topoext perfctr_core perfctr_nb bpext
perfctr_llc mwaitx cpb hw_pstate sme ssbd sev ibpb vmmcall fsgsbase bmi1 avx2
smep bmi2 rdseed adx smap clflushopt sha_ni xsaveopt xsavec xgetbv1 xsaves
clzero irperf xsaveerptr arat npt lbrv svm_lock nrip_save tsc_scale vmcb_clean
flushbyasid decodeassists pausefilter pfthreshold avic v_vmsave_vmload vgif
overflow_recov succor smca

It looks like the OpenMP runtime needs to be taught about the AMD-specific
CPUID leaf 0x8000001E. Or as an ugly fallback, learn topology from
/proc/cpuinfo when leaf 0xb is unavailable?

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