Introduction

This project helps to explore your hardware and achieve the peak performance for your needs.

Enviroment

• OS: ubuntu 20.04
• Compiler: GCC 9.3.0
  • optimization level: -O3
• Platform: x86_x64
• Hardware info:

Architecture:                    x86_64
CPU op-mode(s):                  32-bit, 64-bit
Byte Order:                      Little Endian
Address sizes:                   39 bits physical, 48 bits virtual
CPU(s):                          6
On-line CPU(s) list:             0-5
Thread(s) per core:              1
Core(s) per socket:              6
Socket(s):                       1
Vendor ID:                       GenuineIntel
CPU family:                      6
Model:                           158
Model name:                      Intel(R) Core(TM) i5-8400 CPU @ 2.80GHz
Stepping:                        10
CPU MHz:                         2808.010
BogoMIPS:                        5616.02
Hypervisor vendor:               Microsoft
Virtualization type:             full
L1d cache:                       192 KiB
L1i cache:                       192 KiB
L2 cache:                        1.5 MiB
L3 cache:                        9 MiB
Vulnerability Itlb multihit:     KVM: Vulnerable
Vulnerability L1tf:              Mitigation; PTE Inversion
Vulnerability Mds:               Mitigation; Clear CPU buffers; SMT Host state unknown
Vulnerability Meltdown:          Mitigation; PTI
Vulnerability Spec store bypass: Mitigation; Speculative Store Bypass disabled via prctl and seccomp
Vulnerability Spectre v1:        Mitigation; usercopy/swapgs barriers and __user pointer sanitization
Vulnerability Spectre v2:        Mitigation; Full generic retpoline, IBPB conditional, IBRS_FW, STIBP disabled, RSB filling
Vulnerability Srbds:             Unknown: Dependent on hypervisor status
Vulnerability Tsx async abort:   Not affected
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 xt
                                 opology cpuid pni pclmulqdq ssse3 fma cx16 pcid sse4_1 sse4_2 movbe popcnt aes xsave avx f16c rdrand hypervisor lahf_lm abm 3dnowprefetch invpcid_single pti ssbd
                                 ibrs ibpb stibp fsgsbase bmi1 avx2 smep bmi2 erms invpcid rdseed adx smap clflushopt xsaveopt xsavec xgetbv1 xsaves md_clear flush_l1d arch_capabilities

• Miroarch: Coffee Lake (AVX2)

  • registers: 16 x 256bit
  • cache line size: 64bytes(8 FP64)

• Instruction Timing

  Intrinsics	Instruction	Latency	Throughput
  _mm256_load_pd	vmovapd	7	0.5
  _mm256_store_pd	vmovapd	5	1
  _mm256_fmadd_pd	vfmadd213pd	4	0.5
  _mm256_permute4x64_pd	vpermpd	3	1
  _mm256_permute2f128_pd	vperm2f128	3	1
  _mm256_shuffle_pd	vshufpd	1	1

• Coffee Lake microarch

Theorical Peak Performance

Coffee Lake microarch has two issue ports each has a FMA unit(see the previous diagram), so at most two floating point instructions(add and mul) could be done per-cycle, in addition the CPU supports avx2 extension with 256bit register which could hold 4 FP64(8 FP32) values, as a result 16 FP64 instructions could be executed per-cycle. The CPU could boost it's frequency from 2.8GHz to at most 4GHz, so the peak performance could be 64GFLOPS(FP64).

Also the following formula could be used:

N_CORES * FREQUENCY * FMA * UNITS * (SIZE_OF_VECTOR/64)

for my hardware in single thread

1 * 4 * 2 * 2 * (256/64) = 64

Benchmarks

Single Thread

Method	GFLOPS(FP64)
Theory	64
MKL	56.971941
OpenBlas	51.170771
naive-ijk	1.960400
manual	46.719804