[Bug math/27461] Unixbench/whetstone-double performance regression on glibc2.32

["xuchunmei at linux dot alibaba.com" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=27461

--- Comment #4 from xuchunmei <xuchunmei at linux dot alibaba.com> ---
I tested on another x86 cpu without fma, the hot function is __ieee754_exp_avx
and __ieee754_log_avx, the result shows that glibc2.32 is a little better than
glibc2.28.

on glibc2.32:
Benchmark Run: Tue Mar 02 2021 12:51:38 - 12:51:55
8 CPUs in system; running 8 parallel copies of tests

Double-Precision Whetstone                    28050.2 MWIPS (10.0 s, 1 samples)

System Benchmarks Partial Index              BASELINE       RESULT    INDEX
Double-Precision Whetstone                       55.0      28050.2   5100.0
                                                                   ========
System Benchmarks Index Score (Partial Only)                         5100.0

on glibc2.28:
Benchmark Run: Tue Mar 02 2021 12:53:01 - 12:53:19
8 CPUs in system; running 8 parallel copies of tests

Double-Precision Whetstone                    27715.3 MWIPS (9.5 s, 1 samples)

System Benchmarks Partial Index              BASELINE       RESULT    INDEX
Double-Precision Whetstone                       55.0      27715.3   5039.2
                                                                   ========
System Benchmarks Index Score (Partial Only)                         5039.2

perf data:
glibc2.32:
+   53.99%  whetstone-doubl  whetstone-double   [.] whetstones.constprop.1
+   13.42%  whetstone-doubl  libm-2.32.so       [.] __atan_avx
+    9.95%  whetstone-doubl  libm-2.32.so       [.] __cos_avx
+    7.03%  whetstone-doubl  libm-2.32.so       [.] __ieee754_log_avx
+    6.86%  whetstone-doubl  libm-2.32.so       [.] __ieee754_exp_avx
+    6.44%  whetstone-doubl  libm-2.32.so       [.] __sincos
+    1.13%  whetstone-doubl  libm-2.32.so       [.] exp@@GLIBC_2.29
     0.31%  whetstone-doubl  libm-2.32.so       [.] log@@GLIBC_2.29
     0.22%  whetstone-doubl  [kernel.kallsyms]  [k] __softirqentry_text_start
     0.15%  whetstone-doubl  whetstone-double   [.] log@plt
     0.11%  whetstone-doubl  libm-2.32.so       [.] 0x000000000000f3a4
     0.05%  whetstone-doubl  whetstone-double   [.] sincos@plt
     0.03%  whetstone-doubl  whetstone-double   [.] exp@plt
     0.02%  whetstone-doubl  [kernel.kallsyms]  [k] run_timer_softirq
     0.01%  whetstone-doubl  whetstone-double   [.] cos@plt
     0.01%  whetstone-doubl  whetstone-double   [.] atan@plt
     0.01%  whetstone-doubl  [kernel.kallsyms]  [k] finish_task_switch

glibc2.28:
+   52.14%  whetstone-doubl  whetstone-double    [.] whetstones.constprop.1
+   12.88%  whetstone-doubl  libm-2.28.so        [.] __atan_avx
+   12.64%  whetstone-doubl  libm-2.28.so        [.] __ieee754_log_avx
+    9.85%  whetstone-doubl  libm-2.28.so        [.] __cos_avx
+    6.43%  whetstone-doubl  libm-2.28.so        [.] __sincos
+    5.32%  whetstone-doubl  libm-2.28.so        [.] __ieee754_exp_avx
     0.14%  whetstone-doubl  whetstone-double    [.] __log_finite@plt
     0.14%  whetstone-doubl  whetstone-double    [.] __exp_finite@plt
     0.12%  whetstone-doubl  [kernel.kallsyms]   [k] __softirqentry_text_start
     0.05%  whetstone-doubl  whetstone-double    [.] sincos@plt
     0.01%  whetstone-doubl  [kernel.kallsyms]   [k] run_timer_softirq
     0.01%  whetstone-doubl  [kernel.kallsyms]   [k]
_raw_spin_unlock_irqrestore

cpuinfo:
# lscpu
Architecture:        x86_64
CPU op-mode(s):      32-bit, 64-bit
Byte Order:          Little Endian
CPU(s):              8
On-line CPU(s) list: 0-7
Thread(s) per core:  2
Core(s) per socket:  2
Socket(s):           2
NUMA node(s):        1
Vendor ID:           GenuineIntel
CPU family:          6
Model:               45
Model name:          Intel(R) Xeon(R) CPU E5-2430 0 @ 2.20GHz
Stepping:            7
CPU MHz:             2194.710
BogoMIPS:            4389.42
Virtualization:      VT-x
Hypervisor vendor:   KVM
Virtualization type: full
L1d cache:           32K
L1i cache:           32K
L2 cache:            256K
L3 cache:            15360K
NUMA node0 CPU(s):   0-7
Flags:               fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca
cmov pat pse36 clflush mmx fxsr sse sse2 ss ht syscall nx pdpe1gb rdtscp lm
constant_tsc rep_good nopl cpuid tsc_known_freq pni pclmulqdq vmx ssse3 cx16
pcid sse4_1 sse4_2 x2apic popcnt tsc_deadline_timer aes xsave avx hypervisor
lahf_lm cpuid_fault ibrs ibpb stibp tpr_shadow vnmi flexpriority ept vpid
tsc_adjust xsaveopt

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