point-to-point latency

Reviewed-on: portelli/lattice-benchmarks#5

Grid/Benchmark_Grid.cpp

@@ -264,126 +264,83 @@ class Benchmark
     return;
   }
 
-  static void Latency(void)
+  static void PointToPoint(void)
   {
     int Nloop = 200;
-    int nmu = 0;
 
     Coordinate simd_layout = GridDefaultSimd(Nd, vComplexD::Nsimd());
     Coordinate mpi_layout = GridDefaultMpi();
-    Coordinate shm_layout;
-    GlobalSharedMemory::GetShmDims(mpi_layout, shm_layout);
 
-    for (int mu = 0; mu < Nd; mu++)
-      if (mpi_layout[mu] > 1)
-        nmu++;
-
-    std::vector<double> t_time(Nloop);
-    time_statistics timestat;
-
-    std::cout << GridLogMessage << "Benchmarking Latency to neighbors in " << nmu
-              << " dimensions" << std::endl;
+    std::cout << GridLogMessage << "Benchmarking point-to-point latency" << std::endl;
     grid_small_sep();
-    grid_printf("%5s %7s %15s %15s %15s\n", "dir", "shm", "time (usec)", "std dev",
-                "min");
+    grid_printf("from to      mean(usec)      err        min\n");
 
-    int lat = 8; // dummy lattice size. Not really used.
+    int lat = 8; // dummy lattice size. Not actually used.
     Coordinate latt_size({lat * mpi_layout[0], lat * mpi_layout[1], lat * mpi_layout[2],
                           lat * mpi_layout[3]});
 
     GridCartesian Grid(latt_size, simd_layout, mpi_layout);
-    RealD Nrank = Grid._Nprocessors;
-    RealD Nnode = Grid.NodeCount();
-    RealD ppn = Nrank / Nnode;
 
-    std::vector<HalfSpinColourVectorD *> xbuf(8);
-    std::vector<HalfSpinColourVectorD *> rbuf(8);
-    uint64_t bytes = 8;
-    for (int d = 0; d < 8; d++)
-    {
-      xbuf[d] = (HalfSpinColourVectorD *)acceleratorAllocDevice(bytes);
-      rbuf[d] = (HalfSpinColourVectorD *)acceleratorAllocDevice(bytes);
-    }
+    int ranks;
+    int me;
+    MPI_Comm_size(Grid.communicator, &ranks);
+    MPI_Comm_rank(Grid.communicator, &me);
+    assert(ranks == Grid._Nprocessors);
+    assert(me == Grid._processor);
 
-    double dbytes;
-#define NWARMUP 50
-
-    for (int dir = 0; dir < 8; dir++)
-    {
-      int mu = dir % 4;
-      if (mpi_layout[mu] == 1) // skip directions that are not distributed
-        continue;
-      bool is_shm = mpi_layout[mu] == shm_layout[mu];
-      bool is_partial_shm = !is_shm && shm_layout[mu] != 1;
-
-      std::vector<double> times(Nloop);
-      for (int i = 0; i < NWARMUP; i++)
+    int bytes = 8;
+    void *buf_from = acceleratorAllocDevice(bytes);
+    void *buf_to = acceleratorAllocDevice(bytes);
+    nlohmann::json json_p2p;
+    for (int from = 0; from < ranks; ++from)
+      for (int to = 0; to < ranks; ++to)
       {
-        int xmit_to_rank;
-        int recv_from_rank;
+        if (from == to)
+          continue;
 
-        if (dir == mu)
+        std::vector<double> t_time(Nloop);
+        time_statistics timestat;
+        MPI_Status status;
+
+        for (int i = 0; i < Nloop; ++i)
         {
-          int comm_proc = 1;
-          Grid.ShiftedRanks(mu, comm_proc, xmit_to_rank, recv_from_rank);
+          double start = usecond();
+          if (from == me)
+          {
+            auto err = MPI_Send(buf_from, bytes, MPI_CHAR, to, 0, Grid.communicator);
+            assert(err == MPI_SUCCESS);
+            err = MPI_Recv(buf_to, bytes, MPI_CHAR, to, 0, Grid.communicator, &status);
+            assert(err == MPI_SUCCESS);
+          }
+          if (to == me)
+          {
+            auto err =
+                MPI_Recv(buf_to, bytes, MPI_CHAR, from, 0, Grid.communicator, &status);
+            assert(err == MPI_SUCCESS);
+            err = MPI_Send(buf_from, bytes, MPI_CHAR, from, 0, Grid.communicator);
+            assert(err == MPI_SUCCESS);
+          }
+          double stop = usecond();
+          t_time[i] = stop - start;
         }
-        else
-        {
-          int comm_proc = mpi_layout[mu] - 1;
-          Grid.ShiftedRanks(mu, comm_proc, xmit_to_rank, recv_from_rank);
-        }
-        Grid.SendToRecvFrom((void *)&xbuf[dir][0], xmit_to_rank, (void *)&rbuf[dir][0],
-                            recv_from_rank, bytes);
+        // important: only the 'from' rank has a trustworthy time
+        MPI_Bcast(t_time.data(), Nloop, MPI_DOUBLE, from, Grid.communicator);
+
+        timestat.statistics(t_time);
+        grid_printf("%2d %2d %15.2f %15.1f %15.2f\n", from, to, timestat.mean,
+                    timestat.err, timestat.min);
+        nlohmann::json tmp;
+        tmp["from"] = from;
+        tmp["to"] = to;
+        tmp["time_usec"] = timestat.mean;
+        tmp["time_usec_error"] = timestat.err;
+        tmp["time_usec_max"] = timestat.min;
+        json_p2p.push_back(tmp);
       }
-      for (int i = 0; i < Nloop; i++)
-      {
+    json_results["latency"] = json_p2p;
 
-        dbytes = 0;
-        double start = usecond();
-        int xmit_to_rank;
-        int recv_from_rank;
-
-        if (dir == mu)
-        {
-          int comm_proc = 1;
-          Grid.ShiftedRanks(mu, comm_proc, xmit_to_rank, recv_from_rank);
-        }
-        else
-        {
-          int comm_proc = mpi_layout[mu] - 1;
-          Grid.ShiftedRanks(mu, comm_proc, xmit_to_rank, recv_from_rank);
-        }
-        Grid.SendToRecvFrom((void *)&xbuf[dir][0], xmit_to_rank, (void *)&rbuf[dir][0],
-                            recv_from_rank, bytes);
-        dbytes += bytes;
-
-        double stop = usecond();
-        t_time[i] = stop - start; // microseconds
-      }
-      timestat.statistics(t_time);
-
-      grid_printf("%5d %7s %15.2f %15.1f %15.2f\n", dir,
-                  is_shm           ? "yes"
-                  : is_partial_shm ? "partial"
-                                   : "no",
-                  timestat.mean, timestat.err, timestat.min);
-      nlohmann::json tmp;
-      nlohmann::json tmp_rate;
-      tmp["dir"] = dir;
-      tmp["shared_mem"] = is_shm;
-      tmp["partial_shared_mem"] = is_partial_shm;
-      tmp["time_usec"] = timestat.mean;
-      tmp["time_usec_error"] = timestat.err;
-      tmp["time_usec_max"] = timestat.min;
-      json_results["latency"].push_back(tmp);
-    }
-    for (int d = 0; d < 8; d++)
-    {
-      acceleratorFreeDevice(xbuf[d]);
-      acceleratorFreeDevice(rbuf[d]);
-    }
-
-    return;
+    acceleratorFreeDevice(buf_from);
+    acceleratorFreeDevice(buf_to);
   }
 
   static void Memory(void)
@@ -647,8 +604,6 @@ class Benchmark
 
         FGrid->Broadcast(0, &ncall, sizeof(ncall));
 
-        Dw.ZeroCounters();
-
         time_statistics timestat;
         std::vector<double> t_time(ncall);
         for (uint64_t i = 0; i < ncall; i++)
@@ -843,7 +798,6 @@ class Benchmark
         uint64_t ncall = 500;
 
         FGrid->Broadcast(0, &ncall, sizeof(ncall));
-        Ds.ZeroCounters();
 
         time_statistics timestat;
         std::vector<double> t_time(ncall);
@@ -930,7 +884,7 @@ int main(int argc, char **argv)
   int do_su4 = 1;
   int do_memory = 1;
   int do_comms = 1;
-  int do_latency = 1;
+  int do_p2p = 1;
   int do_flops = 1;
   int Ls = 1;
 
@@ -966,12 +920,12 @@ int main(int argc, char **argv)
     Benchmark::Comms();
   }
 
-  if (do_latency)
+  if (do_p2p)
   {
     grid_big_sep();
-    std::cout << GridLogMessage << " Latency benchmark " << std::endl;
+    std::cout << GridLogMessage << " Point-to-Point benchmark " << std::endl;
     grid_big_sep();
-    Benchmark::Latency();
+    Benchmark::PointToPoint();
   }
 
   if (do_flops)