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Re: Some help needed - further help

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On 2021-09-27 at 17:35, Bonita Montero wrote:
> Am 26.09.2021 um 07:26 schrieb Bonita Montero:
> 
>> So I can adjust the spinning-loop according
>> to pause_singleton::getNsPerPause().
> 
> I dropped it ! I simply made a spinning-loop according to the TSC
> if the CPU has a TSC and it is invariant (these are also invariant
> across sockets !). Reading the TSC can be done at roughly every 10
> nanoseconds my PC (TR3990X, Zen3, Win10, SMT off). It's not accu-
> rate since it might overlap with instruction before or afterwards,
> but accuracy isn't relevant when you spin hundreds of clock-cycles.
> And I changed a single pause per spin loop instead of a row of
> PAUSEs which sum up to 30ns (which is roughly the most common
> value on newer Intel -CPUs). This more eager spinnging may gain
> locking earlier, although it may generate more interconnect-traffic.
> 
> But as I'm using RDTSC: I'm asking myself how fast RDTSC is on
> different CPUs. So I modified my test-program to measure different
> routines to test a loop of 10 RDTSCs per loop. Here it is:
> 
> #include <iostream>
> #include <chrono>
> #include <limits>
> #include <functional>
> #if defined(_MSC_VER)
>      #include <intrin.h>
> #endif
> 
> using namespace std;
> using namespace chrono;
> 
> 
> int main( int argc, char **argv )
> {
>      using bench_fn = function<void(size_t)>;
>      auto bench = []( bench_fn const &fn, size_t nTests, size_t 
> nIterations ) -> double
>      {
>          int64_t nsShortest = numeric_limits<int64_t>::max();
>          for( size_t p = nTests; p; --p )
>          {
>              auto start = high_resolution_clock::now();
>              fn( nIterations );
>              int64_t ns = (int64_t)duration_cast<nanoseconds>( 
> high_resolution_clock::now() - start ).count();
>              nsShortest = ns < nsShortest ? ns : nsShortest;
>          }
>          return (double)nsShortest / (ptrdiff_t)nIterations;
>      };
>      auto rdtscLoop = []( size_t nIterations )
>      {
>          uint64_t TSCs[10];
>          for( ; nIterations; --nIterations )
>              // unfortunately there's no #directive vor REP'ing
> #if defined(_MSC_VER)
>              TSCs[0] += __rdtsc(),
>              TSCs[1] += __rdtsc(),
>              TSCs[2] += __rdtsc(),
>              TSCs[3] += __rdtsc(),
>              TSCs[4] += __rdtsc(),
>              TSCs[5] += __rdtsc(),
>              TSCs[6] += __rdtsc(),
>              TSCs[7] += __rdtsc(),
>              TSCs[8] += __rdtsc(),
>              TSCs[9] += __rdtsc();
> #elif defined(__GNUC__)
>              TSCs[0] += __builtin_ia32_rdtsc(),
>              TSCs[1] += __builtin_ia32_rdtsc(),
>              TSCs[2] += __builtin_ia32_rdtsc(),
>              TSCs[3] += __builtin_ia32_rdtsc(),
>              TSCs[4] += __builtin_ia32_rdtsc(),
>              TSCs[5] += __builtin_ia32_rdtsc(),
>              TSCs[6] += __builtin_ia32_rdtsc(),
>              TSCs[7] += __builtin_ia32_rdtsc(),
>              TSCs[8] += __builtin_ia32_rdtsc(),
>              TSCs[9] += __builtin_ia32_rdtsc();
> #endif
>          uint64_t sum = 0; // prevent optimization
>          for( uint64_t TSC : TSCs )
>              sum += TSC;
>          uint64_t volatile vsum = sum;
>      };
>      static size_t const
>          N_TESTS = 100, // number of tests to get the shortest timing
>          N_ITERATIONS = 500, // iterations of the test-loop
>          N_REPEATS = 10; // REPetitions inside the test-loop
>      double nsPerREP = bench( bench_fn( bind( rdtscLoop, 
> placeholders::_1 ) ), N_TESTS, N_ITERATIONS ) / N_REPEATS;
>      cout << "ns per RDTSC: " << nsPerREP << endl;
> }
> 
> It would be nice if you could compile this on your machine and
> give me the number of the RDTSC-timing here. This would give me
> a hint if what I try is feasible.

I get

ns per RDTSC: 5.42

on my Core i9-9900K 5GHz

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Thread

Some help needed Bonita Montero <Bonita.Montero@gmail.com> - 2021-09-25 16:41 +0200
  Re: Some help needed Paavo Helde <myfirstname@osa.pri.ee> - 2021-09-25 19:51 +0300
    Re: Some help needed Bonita Montero <Bonita.Montero@gmail.com> - 2021-09-25 19:01 +0200
    Re: Some help needed Branimir Maksimovic <branimir.maksimovic@gmail.com> - 2021-09-25 17:20 +0000
  Re: Some help needed Bo Persson <bo@bo-persson.se> - 2021-09-25 19:05 +0200
    Re: Some help needed Bonita Montero <Bonita.Montero@gmail.com> - 2021-09-25 19:14 +0200
    Re: Some help needed Branimir Maksimovic <branimir.maksimovic@gmail.com> - 2021-09-25 17:33 +0000
  Re: Some help needed Branimir Maksimovic <branimir.maksimovic@gmail.com> - 2021-09-25 17:15 +0000
    Re: Some help needed Bonita Montero <Bonita.Montero@gmail.com> - 2021-09-25 19:16 +0200
      Re: Some help needed Branimir Maksimovic <branimir.maksimovic@gmail.com> - 2021-09-25 17:29 +0000
  Re: Some help needed Bonita Montero <Bonita.Montero@gmail.com> - 2021-09-26 07:26 +0200
    Re: Some help needed Branimir Maksimovic <branimir.maksimovic@gmail.com> - 2021-09-26 06:56 +0000
    Re: Some help needed - further help Bonita Montero <Bonita.Montero@gmail.com> - 2021-09-27 17:35 +0200
      Re: Some help needed - further help Bo Persson <bo@bo-persson.se> - 2021-09-27 19:29 +0200

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