Re: volk questions

[Johannes Demel]

Hi Fons,

sorry for the abbreviation PR == Pull Request. A request to merge your 
contribution into the VOLK repository in this case. This includes a 
forum to discuss the specifics and possible improvements before we merge 
your code.

Did your Boost issue get solved? Boost was only required for old VOLK 
and environment versions that did not support `std::filesystem` yet. 
Your kernel versions imply you use a more recent system that supports 
this C++17 feature.
For everyone else, libvolk is still a C library. We only use C++ for 
tests etc.

For reference, these are the CPUs
Intel Core i5-3470
https://www.intel.com/content/www/us/en/products/sku/68316/intel-core-i53470-processor-6m-cache-up-to-3-60-ghz/specifications.html
With SSE and AVX

Intel Core i5-4300U
https://www.intel.com/content/www/us/en/products/sku/76308/intel-core-i54300u-processor-3m-cache-up-to-2-90-ghz/specifications.html
With SSE, AVX, and AVX2

I can't tell from a distance, why VOLK would not select AVX kernels on 
an AVX capable CPU.

For your benchmarking needs:
https://github.com/google/benchmark

This might be a very important section of the docs:
https://github.com/google/benchmark/blob/main/docs/user_guide.md#preventing-optimization
Especially `DoNotOptimize` should be interesting.
It could very well happen, that your code was optimized out.

Cheers
Johannes



On 14.10.23 11:02, Fons Adriaensen wrote:
> Hi Johannes,
>
> Thanks for your response !
>
> > first off, we'd need to know a bit more about your setup. Could you share
> > the versions of VOLK and your host system, e.g. OS, version, etc.
> > Furthermore, do you use a VM, a container, or smth like this?
>
> VOLK was 2.5.0, now upgraded to 3.0.0, same results.
> No VM, container, etc used.
>
> Machine info:
>
> zita1 (desktop)
>
> fons@zita1:~> lscpu
> Architecture:            x86_64
>    CPU op-mode(s):        32-bit, 64-bit
>    Address sizes:         36 bits physical, 48 bits virtual
>    Byte Order:            Little Endian
> CPU(s):                  4
>    On-line CPU(s) list:   0-3
> Vendor ID:               GenuineIntel
>    Model name:            Intel(R) Core(TM) i5-3470 CPU @ 3.20GHz
>      CPU family:          6
>      Model:               58
>      Thread(s) per core:  1
>      Core(s) per socket:  4
>      Socket(s):           1
>      Stepping:            9
>      CPU(s) scaling MHz:  45%
>      CPU max MHz:         3600.0000
>      CPU min MHz:         1600.0000
>      BogoMIPS:            6387.26
>      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 rdtscp lm constant_tsc arch_perfmon pebs bts 
> rep_good nopl
>                           xtopology nonstop_tsc cpuid aperfmperf pni pclmulqdq 
> dtes64
>                           monitor ds_cpl vmx smx est tm2 ssse3 cx16 xtpr pdcm 
> pcid
>                           sse4_1 sse4_2 x2apic popcnt tsc_deadline_timer aes 
> xsave avx
>                           f16c rdrand lahf_lm cpuid_fault epb pti tpr_shadow 
> flexp
>                           riority ept vpid fsgsbase smep erms xsaveopt dtherm 
> ida arat
>                           pln pts vnmi
> Virtualization features:
>    Virtualization:        VT-x
> Caches (sum of all):
>    L1d:                   128 KiB (4 instances)
>    L1i:                   128 KiB (4 instances)
>    L2:                    1 MiB (4 instances)
>    L3:                    6 MiB (1 instance)
> NUMA:
>    NUMA node(s):          1
>    NUMA node0 CPU(s):     0-3
> Vulnerabilities:
>    Gather data sampling:  Not affected
>    Itlb multihit:         KVM: Mitigation: VMX disabled
>    L1tf:                  Mitigation; PTE Inversion; VMX conditional cache 
> flushes, SMT disabled
>    Mds:                   Vulnerable: Clear CPU buffers attempted, no 
> microcode; SMT disabled
>    Meltdown:              Mitigation; PTI
>    Mmio stale data:       Unknown: No mitigations
>    Retbleed:              Not affected
>    Spec rstack overflow:  Not affected
>    Spec store bypass:     Vulnerable
>    Spectre v1:            Mitigation; usercopy/swapgs barriers and __user 
> pointer sanitization
>    Spectre v2:            Mitigation; Retpolines, STIBP disabled, RSB filling, 
> PBRSB-eIBRS Not affected
>    Srbds:                 Vulnerable: No microcode
>    Tsx async abort:       Not affected
>
> fons@zita1:~> uname -a
> Linux zita1 6.5.5-arch1-1 #1 SMP PREEMPT_DYNAMIC Sat, 23 Sep 2023 22:55:13 
> +0000 x86_64 GNU/Linux
>
>
> zita4 (laptop)
>
> Architecture:            x86_64
>    CPU op-mode(s):        32-bit, 64-bit
>    Address sizes:         39 bits physical, 48 bits virtual
>    Byte Order:            Little Endian
> CPU(s):                  4
>    On-line CPU(s) list:   0-3
> Vendor ID:               GenuineIntel
>    Model name:            Intel(R) Core(TM) i5-4300U CPU @ 1.90GHz
>      CPU family:          6
>      Model:               69
>      Thread(s) per core:  2
>      Core(s) per socket:  2
>      Socket(s):           1
>      Stepping:            1
>      CPU(s) scaling MHz:  46%
>      CPU max MHz:         2900.0000
>      CPU min MHz:         800.0000
>      BogoMIPS:            4990.47
>      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 arch_perfmon pebs 
> bts rep_good
>                           nopl xtopology nons top_tsc cpuid aperfmperf pni 
> pclmulqdq dtes64
>                           monitor ds_cpl vmx smx est tm2 ssse3 sdbg fma cx16 
> xtpr pdcm pcid
>                           sse4_1 sse4_2 x2apic movbe popcnt aes xsave avx f16c 
> rdrand lahf_lm
>                           abm cpuid_fault epb invpcid_single pti tpr_shadow 
> vnmi flexpriority
>                           ept vpid ept_ad fsgsbase tsc_adjust bmi1 hle avx2 
> smep bmi2 erms
>                           invpcid rtm xsaveopt dtherm ida arat pln pts
> Virtualization features:
>    Virtualization:        VT-x
> Caches (sum of all):
>    L1d:                   64 KiB (2 instances)
>    L1i:                   64 KiB (2 instances)
>    L2:                    512 KiB (2 instances)
>    L3:                    3 MiB (1 instance)
> NUMA:
>    NUMA node(s):          1
>    NUMA node0 CPU(s):     0-3
> Vulnerabilities:
>    Itlb multihit:         KVM: Mitigation: VMX disabled
>    L1tf:                  Mitigation; PTE Inversion; VMX conditional cache 
> flushes, SMT vulnerable
>    Mds:                   Vulnerable: Clear CPU buffers attempted, no 
> microcode; SMT vulnerable
>    Meltdown:              Mitigation; PTI
>    Mmio stale data:       Unknown: No mitigations
>    Retbleed:              Not affected
>    Spec store bypass:     Vulnerable
>    Spectre v1:            Mitigation; usercopy/swapgs barriers and __user 
> pointer sanitization
>    Spectre v2:            Mitigation; Retpolines, STIBP disabled, RSB filling, 
> PBRSB-eIBRS Not affected
>    Srbds:                 Vulnerable: No microcode
>    Tsx async abort:       Vulnerable: Clear CPU buffers attempted, no 
> microcode; SMT vulnerable
>
> fons@zita4:~> uname -a
> Linux zita4 6.3.2-arch1-1 #1 SMP PREEMPT_DYNAMIC Thu, 11 May 2023 16:40:42 
> +0000 x86_64 GNU/Linux
> (needs an update !)
>
> > Regarding your question, if these functions may be useful to VOLK / GNU
> > Radio. I'd say yes. We'd have to figure out how this may work in practice
> > though. I'd suggest to start with a PR.
>
> PR ?
>
> Ciao,

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