diff --git a/Grid/algorithms/multigrid/BlockCyclicSchurInverse.h b/Grid/algorithms/multigrid/BlockCyclicSchurInverse.h
index c459abfd7..ce00004d1 100644
--- a/Grid/algorithms/multigrid/BlockCyclicSchurInverse.h
+++ b/Grid/algorithms/multigrid/BlockCyclicSchurInverse.h
@@ -397,6 +397,25 @@ public:
               << " gemm min/max " << gmin << "/" << gmax
               << " | ring bytes/rank " << gb << " GB -> " << (ring>0 ? gb/ring : 0.0) << " GB/s/rank (boss)"
               << std::endl;
+    // Ring time decomposed by message size (boss rank; every rank sends the
+    // same sequence of sizes).  Time is wall time inside SendToRecvFrom, so it
+    // includes waiting for the partner -- a bucket whose GB/s is far below the
+    // probe's for the same size is wait, not wire.
+    std::cout << GridLogMessage << "BlockCyclicSumma ring histogram (boss):  size-bucket  msgs  GB  secs  GB/s  %time" << std::endl;
+    std::streamsize oldprec = std::cout.precision();
+    for(int b=0;b<SUMMA.NHIST;b++){
+      if ( !SUMMA.histN[b] ) continue;
+      double sec = SUMMA.histUs[b]/1.0e6, g = SUMMA.histBytes[b]/1.0e9;
+      double lo = (double)(1ull<<b);
+      char sz[32]; if (lo>=1048576) snprintf(sz,32,"%6.1f MB",lo/1048576.); else if (lo>=1024) snprintf(sz,32,"%6.1f KB",lo/1024.); else snprintf(sz,32,"%6.0f B ",lo);
+      std::cout << GridLogMessage << "   >=" << sz
+                << std::setw(8) << SUMMA.histN[b]
+                << std::setw(10) << std::setprecision(3) << g
+                << std::setw(9) << std::setprecision(3) << sec
+                << std::setw(9) << std::setprecision(3) << (sec>0 ? g/sec : 0.0)
+                << std::setw(8) << std::setprecision(3) << (ring>0 ? 100.0*sec/ring : 0.0) << std::endl;
+    }
+    std::cout.precision(oldprec);
   }
 };
 
diff --git a/Grid/algorithms/multigrid/BlockCyclicSumma.h b/Grid/algorithms/multigrid/BlockCyclicSumma.h
index 33f3cefa0..ab5e7a876 100644
--- a/Grid/algorithms/multigrid/BlockCyclicSumma.h
+++ b/Grid/algorithms/multigrid/BlockCyclicSumma.h
@@ -143,7 +143,14 @@ public:
   deviceVector<ComplexD> Bbuf;
   double   tAlloc=0, tPack=0, tRingA=0, tRingB=0, tGemm=0;
   uint64_t bytesRing=0, nRingMsg=0, nMultiply=0, nGemm=0;
-  void ResetTelemetry(void){ tAlloc=tPack=tRingA=tRingB=tGemm=0; bytesRing=nRingMsg=nMultiply=nGemm=0; }
+  // Per-message-size histogram (bucket = floor(log2 bytes)): count, bytes,
+  // microseconds -- decomposes the ring time by packet size so a low average
+  // GB/s can be attributed (many small latency-bound messages vs slow large
+  // ones vs partner-wait).  The 8 MB probe runs at 11-20 GB/s; SUMMA averaged 2.
+  static const int NHIST=48;
+  uint64_t histN[NHIST]={0}, histBytes[NHIST]={0}; double histUs[NHIST]={0};
+  void HistAdd(uint64_t bytes, double us){ int b=0; while((bytes>>b)>1) b++; histN[b]++; histBytes[b]+=bytes; histUs[b]+=us; }
+  void ResetTelemetry(void){ tAlloc=tPack=tRingA=tRingB=tGemm=0; bytesRing=nRingMsg=nMultiply=nGemm=0; for(int b=0;b<NHIST;b++){histN[b]=histBytes[b]=0; histUs[b]=0;} }
 
   static int Overlap(int64_t a0,int64_t a1,int64_t b0,int64_t b1)
   { return (a0 < b1) && (b0 < a1); }
@@ -273,9 +280,11 @@ public:
         for(int t=1;t<Pc;t++){
           int cs = (pcol - t + 1 + Pc*Pc) % Pc;
           int cr = (pcol - t     + Pc*Pc) % Pc;
+          double tm = usecond();
           grid->SendToRecvFrom((void *)(&Abuf[0]+slotA*cs), dest,
                                (void *)(&Abuf[0]+slotA*cr), src,
                                slotA*sizeof(ComplexD));
+          HistAdd(slotA*sizeof(ComplexD), usecond()-tm);
           bytesRing += slotA*sizeof(ComplexD); nRingMsg++;
         }
         tRingA += usecond();
@@ -291,9 +300,11 @@ public:
         for(int t=1;t<Pr;t++){
           int rs = (prow - t + 1 + Pr*Pr) % Pr;
           int rr = (prow - t     + Pr*Pr) % Pr;
+          double tm = usecond();
           grid->SendToRecvFrom((void *)(&Bbuf[0]+slotB*rs), dest,
                                (void *)(&Bbuf[0]+slotB*rr), src,
                                slotB*sizeof(ComplexD));
+          HistAdd(slotB*sizeof(ComplexD), usecond()-tm);
           bytesRing += slotB*sizeof(ComplexD); nRingMsg++;
         }
         tRingB += usecond();