device: fine tune MI200/MI250 simple protocol performance

With Simple protocol, unroll factor of 4 offers better
performance for most of the collectives (on MI200. MI250, and
MI300) except large message allreduce with Ring algorithm
on MI250 and MI200). This PR changes the default unroll factor
to 4 while adding fine tuning for reduction operations.

src/collectives/device/common.h

@@ -11,11 +11,7 @@
 #include "collectives.h"
 #include "devcomm.h"
 
-#if defined(__gfx940__)
 #define COLL_UNROLL 4
-#else
-#define COLL_UNROLL 2
-#endif
 
 #define NCCL_MAX_DEV_ARITY (NCCL_MAX_TREE_ARITY-1)  // Using balanced tree instead of split tree
 

src/collectives/device/common_kernel.h

@@ -214,10 +214,17 @@ __device__ __forceinline__ void reduceCopy(
     if (lane < nDsts) aligned &= 0 == cvta_to_global(dstPtrs[lane]) % (BigPackSize + !BigPackSize);
     aligned = !(__any(!aligned));
     if (aligned) {
+#if defined(__gfx90a__)
+      reduceCopyPacks<RedFn, T, ((MinSrcs > 1) ? 2 : Unroll), BigPackSize,
+        MultimemSrcs, MinSrcs, MaxSrcs, MultimemDsts, MinDsts, MaxDsts, PreOpSrcs>
+        (nThreads, thread, redArg, preOpArgs, postOp,
+         nSrcs, srcPtrs, nDsts, dstPtrs, nBytesBehind, nBytesAhead);
+#else
       reduceCopyPacks<RedFn, T, Unroll*((MinSrcs == 1 && MinDsts == 1) ? 2 : 1), BigPackSize,
         MultimemSrcs, MinSrcs, MaxSrcs, MultimemDsts, MinDsts, MaxDsts, PreOpSrcs>
         (nThreads, /*&*/thread, redArg, preOpArgs, postOp,
          nSrcs, srcPtrs, nDsts, dstPtrs, /*&*/nBytesBehind, /*&*/nBytesAhead);
+#endif
       if (nBytesAhead == 0) return;
 
       reduceCopyPacks<RedFn, T, /*Unroll=*/1, BigPackSize,
@@ -228,10 +235,24 @@ __device__ __forceinline__ void reduceCopy(
     }
   }
 
+#if defined(__gfx90a__)
+  if (MinSrcs > 1) {
+    reduceCopyPacks<RedFn, T, Unroll/2*(16/sizeof(T))/2, sizeof(T),
+    MultimemSrcs, MinSrcs, MaxSrcs, MultimemDsts, MinDsts, MaxDsts, PreOpSrcs>
+    (nThreads, thread, redArg, preOpArgs, postOp,
+     nSrcs, srcPtrs, nDsts, dstPtrs, nBytesBehind, nBytesAhead);
+  } else {
+    reduceCopyPacks<RedFn, T, Unroll*(16/sizeof(T))/2, /*BytePerPack=*/sizeof(T),
+    MultimemSrcs, MinSrcs, MaxSrcs, MultimemDsts, MinDsts, MaxDsts, PreOpSrcs>
+    (nThreads, /*&*/thread, redArg, preOpArgs, postOp,
+     nSrcs, srcPtrs, nDsts, dstPtrs, /*&*/nBytesBehind, /*&*/nBytesAhead);
+  }
+#else
   reduceCopyPacks<RedFn, T, Unroll*(16/sizeof(T))/2, /*BytePerPack=*/sizeof(T),
     MultimemSrcs, MinSrcs, MaxSrcs, MultimemDsts, MinDsts, MaxDsts, PreOpSrcs>
     (nThreads, /*&*/thread, redArg, preOpArgs, postOp,
      nSrcs, srcPtrs, nDsts, dstPtrs, /*&*/nBytesBehind, /*&*/nBytesAhead);
+#endif
   if (nBytesAhead == 0) return;
 
   reduceCopyPacks<RedFn, T, /*Unroll=*/1, /*BytePerPack=*/sizeof(T),