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From: Bonita Montero <Bonita.Montero@gmail.com>
Newsgroups: comp.lang.c,comp.lang.c++
Subject: Re: My PC's cores can synchronize to about 1.000 clock cycles
 accuracy
Followup-To: comp.lang.c++
Date: Fri, 13 Sep 2024 18:49:51 +0200
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Sorry, wrong newsgroup.

Am 13.09.2024 um 18:45 schrieb Bonita Montero:
> #include <iostream>
> #include <barrier>
> #include <thread>
> #include <vector>
> #if defined(_WIN32)
>      #include <intrin.h>
> #elif defined(__linux__)
>      #include <x86intrin.h>
> #endif
> 
> using namespace std;
> 
> int main()
> {
>      unsigned hc = thread::hardware_concurrency();
>      barrier bar( hc );
>      atomic_uint synch( hc );
>      atomic_uint64_t zero( 0 );
>      atomic_int64_t diffs( 0 );
>      auto thr = [&]()
>      {
>          int64_t sum = 0;
>          for( unsigned t = 1'000; t; --t )
>          {
>              bar.arrive_and_wait();
>              if( synch.fetch_sub( 1, memory_order_relaxed ) > 1 )
>                  while( synch.load( memory_order_relaxed ) );
>              uint64_t tsc = __rdtsc(), expected = 0;
>              if( !zero.compare_exchange_weak( expected, tsc, 
> memory_order_relaxed, memory_order_relaxed ) )
>                  sum += abs( (int64_t)(expected - tsc) );
>              bar.arrive_and_wait();
>              synch.store( hc );
>              zero.store( 0, memory_order_relaxed );
>          }
>          diffs.fetch_add( sum, memory_order_relaxed );
>      };
>      vector<jthread> threads;
>      threads.reserve( hc - 1 );
>      for( unsigned t = hc - 1; t; --t )
>          threads.emplace_back( thr );
>      thr();
>      threads.resize( 0 );
>      cout << (double)diffs.load( memory_order_relaxed ) / (1'000.0 * hc) 
> << endl;
> }
> 
> My PC is a AMD 7950X 16-core system.
>