diff --git a/makefiles/common.mk b/makefiles/common.mk
index 1a1c2b6..0c0d04a 100644
--- a/makefiles/common.mk
+++ b/makefiles/common.mk
@@ -31,13 +31,17 @@ CUDA8_GENCODE = -gencode=arch=compute_35,code=sm_35 \
                 -gencode=arch=compute_61,code=sm_61
 CUDA9_GENCODE = -gencode=arch=compute_70,code=sm_70
 CUDA11_GENCODE = -gencode=arch=compute_80,code=sm_80
+CUDA11_8_GENCODE = -gencode=arch=compute_90,code=sm_90
 
 CUDA8_PTX     = -gencode=arch=compute_61,code=compute_61
 CUDA9_PTX     = -gencode=arch=compute_70,code=compute_70
 CUDA11_PTX    = -gencode=arch=compute_80,code=compute_80
+CUDA11_8_PTX  = -gencode=arch=compute_90,code=compute_90
 
-# Include Ampere support if we're using CUDA11 or above
-ifeq ($(shell test "0$(CUDA_MAJOR)" -ge 11; echo $$?),0)
+ifeq ($(shell test "0$(CUDA_MAJOR)" -eq 11 -a "0$(CUDA_MINOR)" -ge 8 -o "0$(CUDA_MAJOR)" -gt 11; echo $$?),0)
+# Include Hopper support if we're using CUDA11.8 or above
+  NVCC_GENCODE ?= $(CUDA8_GENCODE) $(CUDA9_GENCODE) $(CUDA11_GENCODE) $(CUDA11_8_GENCODE) $(CUDA11_8_PTX)
+else ifeq ($(shell test "0$(CUDA_MAJOR)" -ge 11; echo $$?),0)
   NVCC_GENCODE ?= $(CUDA8_GENCODE) $(CUDA9_GENCODE) $(CUDA11_GENCODE) $(CUDA11_PTX)
 # Include Volta support if we're using CUDA9 or above
 else ifeq ($(shell test "0$(CUDA_MAJOR)" -ge 9; echo $$?),0)
@@ -45,7 +49,7 @@ else ifeq ($(shell test "0$(CUDA_MAJOR)" -ge 9; echo $$?),0)
 else
   NVCC_GENCODE ?= $(CUDA8_GENCODE) $(CUDA8_PTX)
 endif
-#$(info NVCC_GENCODE is ${NVCC_GENCODE})
+$(info NVCC_GENCODE is ${NVCC_GENCODE})
 
 CXXFLAGS   := -DCUDA_MAJOR=$(CUDA_MAJOR) -DCUDA_MINOR=$(CUDA_MINOR) -fPIC -fvisibility=hidden \
               -Wall -Wno-unused-function -Wno-sign-compare -std=c++11 -Wvla \
diff --git a/makefiles/version.mk b/makefiles/version.mk
index 55fa6cc..977d763 100644
--- a/makefiles/version.mk
+++ b/makefiles/version.mk
@@ -1,6 +1,6 @@
 ##### version
 NCCL_MAJOR   := 2
-NCCL_MINOR   := 14
-NCCL_PATCH   := 3
+NCCL_MINOR   := 15
+NCCL_PATCH   := 1
 NCCL_SUFFIX  :=
 PKG_REVISION := 1
diff --git a/src/channel.cc b/src/channel.cc
index 9587008..c1254f1 100644
--- a/src/channel.cc
+++ b/src/channel.cc
@@ -27,7 +27,7 @@ ncclResult_t initChannel(struct ncclComm* comm, int channelId) {
   NCCLCHECK(ncclCudaCallocAsync(&channel->devRingUserRanks, nRanks, comm->deviceStream.stream));
   ncclCommPushCudaFree(comm, channel->devRingUserRanks);
 
-  NCCLCHECK(ncclStrongStreamRelease(ncclCudaGraphNull(), &comm->deviceStream));
+  NCCLCHECK(ncclStrongStreamRelease(ncclCudaGraphNone(), &comm->deviceStream));
 
   for (int r=0; r < nRanks+1; ++r) {
     for (int b=0; b < NCCL_MAX_CONNS; b++) {
diff --git a/src/enqueue.cc b/src/enqueue.cc
index 7c6d835..0db55bf 100644
--- a/src/enqueue.cc
+++ b/src/enqueue.cc
@@ -940,14 +940,33 @@ ncclResult_t ncclLaunchPrepare(struct ncclComm* comm) {
     struct ncclKernelPlan* planHead = ncclIntruQueueHead(&comm->planQueue);
     comm->unlaunchedPlansHead = planHead;
 
+    // Semantically we want these dependencies for the kernels launched:
+    //   1. Launch host task on hostStream.
+    //   2. Launch kernel, depends on all of {deviceStream, hostStream, userStream[i]...}
+    //   3. {deviceStream, userStream[i]...} depend on kernel.
+    // We achieve this by:
+    //   1. userStream[0] waits on deviceStream
+    //   2. deviceStream waits on each of userStream[1...]
+    //   3. host task launch on hostStream
+    //   4. userStream[0] waits on hostStream
+    //   5. kernel launch on userStream[0]
+    //   6. deviceStream waits on userStream[0]
+    //   7. userStream[1...] each waits on deviceStream
+    // The two-level fan-in fan-out is because ncclStrongStreamWaitStream() requires
+    // at least one of the two streams to be strong-stream.
+    cudaStream_t launchStream = tasks->streams->stream;
     NCCLCHECKGOTO(ncclStrongStreamAcquire(tasks->capturingGraph, &comm->deviceStream), result, failure);
 
-    // Create dependency for nccl device work on user streams.
-    for (struct ncclCudaStreamList* l=tasks->streams; l != nullptr; l = l->next) {
+    // Create dependency for device stream on user streams. First from extra user
+    // streams to deviceStream. Then deviceStream to first user stream.
+    for (struct ncclCudaStreamList* l=tasks->streams->next; l != nullptr; l = l->next) {
       NCCLCHECKGOTO(ncclStrongStreamWaitStream(tasks->capturingGraph, &comm->deviceStream, l->stream), result, failure);
     }
+    NCCLCHECKGOTO(ncclStrongStreamWaitStream(tasks->capturingGraph, launchStream, &comm->deviceStream), result, failure);
 
     if (persistent || comm->persistentRefs != 0) {
+      // We have to launch host tasks to push proxy args. We are careful to only
+      // do this if necessary since host tasks impose a high performance cost in CUDA.
       bool acquired = false;
       for (struct ncclKernelPlan* plan=planHead; plan != nullptr; plan = plan->next) {
         if (plan->hasProxyOps) {
@@ -959,6 +978,8 @@ ncclResult_t ncclLaunchPrepare(struct ncclComm* comm) {
         }
       }
       if (acquired) {
+        // Make to-be-launched kernels dependent on just-launched host stream tasks.
+        NCCLCHECKGOTO(ncclStrongStreamWaitStream(tasks->capturingGraph, launchStream, &comm->hostStream), result, failure);
         NCCLCHECKGOTO(ncclStrongStreamRelease(tasks->capturingGraph, &comm->hostStream), result, failure);
       }
     }
@@ -984,14 +1005,67 @@ ncclResult_t ncclLaunchKernelBefore_NoUncapturedCuda(struct ncclComm* comm, stru
   return ncclSuccess;
 }
 
+#if CUDART_VERSION >= 11080
+#define NCCL_MAX_CGA_CLUSTER_SIZE 8
+NCCL_PARAM(CGAClusterSize, "CGA_CLUSTER_SIZE", 0);
+#endif
+
 ncclResult_t ncclLaunchKernel(struct ncclComm* comm, struct ncclKernelPlan* plan) {
   struct ncclTasks* tasks = &comm->tasks;
+  void *fn = plan->kernelFn;
+  cudaStream_t launchStream = tasks->streams->stream;
   dim3 grid = {(unsigned)plan->channelCount, 1, 1};
   dim3 block = {(unsigned)plan->threadPerBlock, 1, 1};
   void *args[3] = {&comm->devComm, &plan->channelMask, &plan->workHead};
-  NCCLCHECK(ncclStrongStreamLaunchKernel(
-    tasks->capturingGraph, &comm->deviceStream, plan->kernelFn, grid, block, args, 0
-  ));
+
+  #if CUDART_VERSION >= 11080
+  int driverVersion;
+  NCCLCHECK(ncclCudaDriverVersion(&driverVersion));
+
+  unsigned int clusterSize = 0;
+  clusterSize = ncclParamCGAClusterSize();
+  if (clusterSize > NCCL_MAX_CGA_CLUSTER_SIZE) {
+    static bool warned = false;
+    if (warned == false) {
+      WARN("NCCL_CGA_CLUSTER_SIZE value %d is too big. Limiting value to %d.",
+           clusterSize, NCCL_MAX_CGA_CLUSTER_SIZE);
+      warned = true;
+    }
+    clusterSize = NCCL_MAX_CGA_CLUSTER_SIZE;
+  }
+
+  if (clusterSize && driverVersion >= 11080) {
+    cudaLaunchConfig_t launchConfig = {0};
+    cudaLaunchAttribute launchAttrs[2];
+    /* Cooperative Group Array (CGA)
+     * On sm90 and later we have an extra level of hierarchy where we
+     * can group together several blocks within the Grid, called
+     * Thread Block Clusters.
+     * Clusters enable multiple thread blocks running concurrently
+     * across multiple SMs to synchronize and collaboratively fetch
+     * and exchange data. A cluster of blocks are guaranteed to be
+     * concurrently scheduled onto a group of SMs.
+     * The maximum value is 8 and it must be divisible into the grid dimensions
+     */
+    // Grid dimension must be divisible by clusterSize
+    if (grid.x % clusterSize) clusterSize = 1;
+    launchAttrs[0].id = cudaLaunchAttributeClusterDimension;
+    launchAttrs[0].val.clusterDim = {clusterSize, 1, 1};
+    launchAttrs[1].id = cudaLaunchAttributeClusterSchedulingPolicyPreference;
+    launchAttrs[1].val.clusterSchedulingPolicyPreference = cudaClusterSchedulingPolicySpread;
+
+    launchConfig.gridDim = grid;
+    launchConfig.blockDim = block;
+    launchConfig.attrs = launchAttrs;
+    launchConfig.numAttrs = sizeof(launchAttrs)/sizeof(launchAttrs[0]);
+    launchConfig.stream = launchStream;
+
+    CUDACHECK(cudaLaunchKernelExC(&launchConfig, fn, args));
+    return ncclSuccess;
+  }
+  #endif
+  // Standard kernel launch
+  CUDACHECK(cudaLaunchKernel(fn, grid, block, args, 0, launchStream));
   return ncclSuccess;
 }
 
@@ -1017,17 +1091,21 @@ ncclResult_t ncclLaunchFinish(struct ncclComm* comm) {
     // Reset queue to empty without destroying plans since those will be sent
     // back to us for reclaiming via callbackQueue.
     ncclIntruQueueConstruct(&comm->planQueue);
-    // Close strong stream "transaction" encompassing cuda launches
-    NCCLCHECKGOTO(ncclStrongStreamRelease(tasks->capturingGraph, &comm->deviceStream), result, resume1);
+    cudaStream_t launchStream = tasks->streams->stream; // First user stream gets launch
+    // Create dependency for deviceStream on launchStream.
+    NCCLCHECKGOTO(ncclStrongStreamWaitStream(tasks->capturingGraph, &comm->deviceStream, launchStream), result, resume1);
   resume1:
-    // Create dependency for user streams on nccl device work.
-    struct ncclCudaStreamList* sl = tasks->streams;
-    tasks->streams = nullptr; // reset streams to empty
+    // Create dependency for other user streams (skip launch stream).
+    struct ncclCudaStreamList* sl = tasks->streams->next;
+    tasks->streams = nullptr; // Reset comm->tasks.streams to empty.
     while (sl != nullptr) {
       NCCLCHECKGOTO(ncclStrongStreamWaitStream(tasks->capturingGraph, sl->stream, &comm->deviceStream), result, resume2);
     resume2:
       sl = sl->next;
     }
+    // Release device stream as acquired in ncclLaunchPrepare()
+    NCCLCHECKGOTO(ncclStrongStreamRelease(tasks->capturingGraph, &comm->deviceStream), result, resume3);
+  resume3:;
   }
   return result;
 }
@@ -1364,12 +1442,12 @@ static ncclResult_t taskAppend(struct ncclComm* comm, struct ncclInfo const* inf
           NCCLCHECK(ncclChannelComputeFromBase(comm, channelBaseId, c, &channelId));
           if (isSendNotRecv) {
             if (comm->channels[channelId].peers[peer].send[1].connected == 0) { // P2P uses only 1 connector
-              comm->connectSend[peer] |= (1<<channelId);
+              comm->connectSend[peer] |= (1UL<<channelId);
               ncclGroupCommPreconnect(comm);
             }
           } else {
             if (comm->channels[channelId].peers[peer].recv[1].connected == 0) { // P2P uses only 1 connector
-              comm->connectRecv[peer] |= (1<<channelId);
+              comm->connectRecv[peer] |= (1UL<<channelId);
               ncclGroupCommPreconnect(comm);
             }
           }
@@ -1429,6 +1507,7 @@ static ncclResult_t taskAppend(struct ncclComm* comm, struct ncclInfo const* inf
       }
       if (l->stream == info->stream)
         break; // Already seen stream.
+      l = l->next;
     }
   }
   return ncclSuccess;
diff --git a/src/graph/paths.cc b/src/graph/paths.cc
index f8918b1..01f1582 100644
--- a/src/graph/paths.cc
+++ b/src/graph/paths.cc
@@ -399,6 +399,19 @@ ncclResult_t ncclTopoCheckGdr(struct ncclTopoSystem* system, int64_t busId, int
   return ncclSuccess;
 }
 
+// Set to 0 to disable the flush on Hopper when using GDR
+NCCL_PARAM(NetForceFlush, "NET_FORCE_FLUSH", 1);
+
+// Determine whether we need to flush the GDR recv buffers
+ncclResult_t ncclTopoNeedFlush(struct ncclTopoSystem* system, int64_t busId, int* flush) {
+  int g;
+  NCCLCHECK(ncclTopoIdToIndex(system, GPU, busId, &g));
+  struct ncclTopoNode* gpu = system->nodes[GPU].nodes+g;
+  // Flush is required on Ampere and earlier
+  *flush = gpu->gpu.cudaCompCap < 90 ? 1 : ncclParamNetForceFlush();
+  return ncclSuccess;
+}
+
 NCCL_PARAM(NetDisableIntra, "NET_DISABLE_INTRA", 0);
 
 // Check whether going through the network would be faster than going through P2P/SHM.
diff --git a/src/graph/search.cc b/src/graph/search.cc
index 27a8e43..eb0b7dd 100644
--- a/src/graph/search.cc
+++ b/src/graph/search.cc
@@ -727,7 +727,7 @@ ncclResult_t ncclTopoGetXmlFromGraphs(int ngraphs, struct ncclTopoGraph** graphs
 }
 
 float speedArrayIntra[] = { 44.0, 30.0, 22.0, 18.0, 15.0, 12.0, 10.0, 9.0, 7.0, 6.0, 5.0, 4.0, 3.0 };
-float speedArrayInter[] = { 48.0, 30.0, 24.0, 22.0, 18.0, 15.0, 12.0, 10.0, 9.0, 7.0, 6.0, 5.0, 4.0, 3.0, 2.4, 1.2, 0.24, 0.12 };
+float speedArrayInter[] = { 48.0, 30.0, 28.0, 24.0, 22.0, 18.0, 15.0, 12.0, 10.0, 9.0, 7.0, 6.0, 5.0, 4.0, 3.0, 2.4, 1.2, 0.24, 0.12 };
 #define NSPEEDSINTRA (sizeof(speedArrayIntra)/sizeof(float))
 #define NSPEEDSINTER (sizeof(speedArrayInter)/sizeof(float))
 
diff --git a/src/graph/tuning.cc b/src/graph/tuning.cc
index bc5e969..07a2104 100644
--- a/src/graph/tuning.cc
+++ b/src/graph/tuning.cc
@@ -72,10 +72,24 @@ static float hwLat [3][NCCL_NUM_ALGORITHMS][NCCL_NUM_PROTOCOLS] =
     /* CollNetDirect (Simple)*/ { 0, 0, 10.7 }, /* CollNetChain (Simple)*/ { 0, 0, 10.7 } }
 };
 
+/* Array indexes used below */
+#define VOLTA_COMPCAP_IDX 0
+#define AMPERE_COMPCAP_IDX 1
+#define HOPPER_COMPCAP_IDX 2
+
 // LL128 max BW per channel
 static const double ll128MaxBwPerCh = 20.0;
-static const double llMaxBws[2][3] = { /* Volta-N1/Intel-N2/Intel-N4) */ {39.0, 39.0, 20.4}, /* Ampere-N1/AMD-N2/AMD-N4) */ {87.7, 22.5 /*avg of ring & tree*/, 19.0} };
-static const double perChMaxTreeBws[2][3] = { /* Volta (N1/N2/N4) */ {26.5, 18.5, 10.0}, /* Ampere (N1/N2/N4) */ {24.0, 23.6, 17.8} };
+static const double llMaxBws[3][3] = {
+  /* Volta-N1/Intel-N2/Intel-N4) */ {39.0, 39.0, 20.4},
+  /* Ampere-N1/AMD-N2/AMD-N4) */ {87.7, 22.5 /*avg of ring & tree*/, 19.0},
+  /* Hopper-N1/AMD-N2/AMD-N4) */ {87.7, 22.5 /*avg of ring & tree*/, 19.0}
+};
+
+static const double perChMaxTreeBws[3][3] = {
+  /* Volta (N1/N2/N4) */ {26.5, 18.5, 10.0},
+  /* Ampere (N1/N2/N4) */ {24.0, 23.6, 17.8},
+  /* Hopper (N1/N2/N4) */ {24.0, 23.6, 17.8},
+};
 
 ncclResult_t ncclTopoTuneModel(struct ncclComm* comm, int minCompCap, int maxCompCap, struct ncclTopoGraph* treeGraph, struct ncclTopoGraph* ringGraph, struct ncclTopoGraph* collNetGraph) {
   int simpleDefaultThreads = (ringGraph->bwIntra*ringGraph->nChannels <= PCI_BW) ? 256 : NCCL_SIMPLE_MAX_NTHREADS;
@@ -94,14 +108,14 @@ ncclResult_t ncclTopoTuneModel(struct ncclComm* comm, int minCompCap, int maxCom
   int nRanks = comm->nRanks;
   if (nRanks <= 1) return ncclSuccess;
 
-  int compCap80 = minCompCap == 80 && maxCompCap == 80 ? 1 : 0;
+  int compCapIndex = (minCompCap == 80 && maxCompCap == 80) ? AMPERE_COMPCAP_IDX : ((minCompCap == 90 && maxCompCap == 90) ? HOPPER_COMPCAP_IDX : VOLTA_COMPCAP_IDX);
   int cpuArch, cpuVendor, cpuModel;
   NCCLCHECK(ncclTopoCpuType(comm->topo, &cpuArch, &cpuVendor, &cpuModel));
   int index2 = nNodes <= 2 ? nNodes-1 : 2;
   // LL: for single node, we look at GPU type; for multi-node, we look at CPU type
-  int index1 = nNodes == 1 ? compCap80 : cpuVendor == NCCL_TOPO_CPU_VENDOR_AMD ? 1 : 0;
+  int index1 = nNodes == 1 ? compCapIndex : cpuVendor == NCCL_TOPO_CPU_VENDOR_AMD ? 1 : 0;
   double llMaxBw = llMaxBws[index1][index2];
-  double perChMaxTreeBw = perChMaxTreeBws[compCap80][index2];
+  double perChMaxTreeBw = perChMaxTreeBws[compCapIndex][index2];
   // De-penalize Tree/Simple latency on Power systems to favor Tree than Ring
   if (cpuArch == NCCL_TOPO_CPU_ARCH_POWER) hwLat[NCCL_HW_PCI][NCCL_ALGO_TREE][NCCL_PROTO_SIMPLE] = hwLat[NCCL_HW_PCI][NCCL_ALGO_RING][NCCL_PROTO_SIMPLE];
   float ppn = (float)nRanks / nNodes; // if ppn < 2, then we are sending/receiving at the same GPU through the NIC, apply some bw discount
@@ -128,7 +142,7 @@ ncclResult_t ncclTopoTuneModel(struct ncclComm* comm, int minCompCap, int maxCom
         float busBw = graphs[a]->nChannels * bw;
 
         // Various model refinements
-        if (compCap80) busBw = std::min(busBw, 235.0f);
+        if (compCapIndex == AMPERE_COMPCAP_IDX) busBw = std::min(busBw, 235.0f);
         if (a == NCCL_ALGO_RING && p == NCCL_PROTO_LL) { busBw = std::min(llMaxBw, busBw * ((nNodes > 1 || coll == ncclFuncAllReduce || coll == ncclFuncReduce) ? 1.0/4.0 : 1.0/3.0)); }
         if (a == NCCL_ALGO_RING && p == NCCL_PROTO_LL128) busBw = std::min(busBw * (ppn < 2 ? 0.7 : 0.92 /*120.0/128.0*/), ll128MaxBwPerCh*graphs[a]->nChannels);
         if (a == NCCL_ALGO_TREE) busBw = std::min(busBw*.92, graphs[a]->nChannels*perChMaxTreeBw);
@@ -136,13 +150,13 @@ ncclResult_t ncclTopoTuneModel(struct ncclComm* comm, int minCompCap, int maxCom
         if (a == NCCL_ALGO_TREE && p == NCCL_PROTO_LL128) busBw = std::min(busBw * (nNodes == 1 ? 7.0/9.0 : 120.0/128.0), ll128MaxBwPerCh*graphs[a]->nChannels);
         if (a == NCCL_ALGO_COLLNET_DIRECT && p != NCCL_PROTO_SIMPLE) busBw = 0;  // Not used
         if (a == NCCL_ALGO_COLLNET_CHAIN && p != NCCL_PROTO_SIMPLE) busBw = 0;  // Not used
-	if (a == NCCL_ALGO_COLLNET_DIRECT && p == NCCL_PROTO_SIMPLE) {
+        if (a == NCCL_ALGO_COLLNET_DIRECT && p == NCCL_PROTO_SIMPLE) {
           // Collnet+Direct requires all GPUs to have a local NIC to work at full speed
           float factor = ppn / (1.0*graphs[a]->nChannels); // GPU/NIC ratio
-	  factor -= (factor-1)/2;
+          factor -= (factor-1)/2;
           busBw /= factor;
-	}
-	if (a == NCCL_ALGO_COLLNET_CHAIN && p == NCCL_PROTO_SIMPLE) busBw *= .75;
+        }
+        if (a == NCCL_ALGO_COLLNET_CHAIN && p == NCCL_PROTO_SIMPLE) busBw *= .75;
 
         // Convert bus BW to algorithm BW
         float ratio = (a != NCCL_ALGO_RING) ? .5 : (1.0 * nRanks) / nsteps;
@@ -212,9 +226,9 @@ ncclResult_t ncclTopoTuneModel(struct ncclComm* comm, int minCompCap, int maxCom
   for (int c=0; c<NCCL_NUM_FUNCTIONS; c++) for (int a=0; a<NCCL_NUM_ALGORITHMS; a++) for (int p=0; p<NCCL_NUM_PROTOCOLS; p++) {
     int pEnable = protoEnable[p];
     if (pEnable == 2 && p == NCCL_PROTO_LL128) {
-      // Enable LL128 by default only on Volta/Ampere+NVLink. Other cases are not tested and may cause silent data corruption.
+      // Enable LL128 by default only on Volta/Ampere/Hopper+NVLink. Other cases are not tested and may cause silent data corruption.
       pEnable = (graphs[a]->typeInter <= PATH_PXB) && graphs[a]->typeIntra <= PATH_NVL &&
-        ((minCompCap == 70 && maxCompCap == 70) || (minCompCap == 80 && maxCompCap == 80)) ? 1 : 0;
+        ((minCompCap == 70 && maxCompCap == 70) || (minCompCap == 80 && maxCompCap == 80) || (minCompCap == 90 && maxCompCap == 90)) ? 1 : 0;
     }
     if (pEnable == 0) comm->bandwidths[c][a][p] = 0;
     // Only disable algo for Allreduce since others only have one
diff --git a/src/graph/xml.cc b/src/graph/xml.cc
index 838a7f5..316d20f 100644
--- a/src/graph/xml.cc
+++ b/src/graph/xml.cc
@@ -628,7 +628,7 @@ ncclResult_t ncclTopoGetXmlFromGpu(struct ncclXmlNode* pciNode, nvmlDevice_t nvm
   NCCLCHECK(xmlGetSub(gpuNode, "nvlink", &nvlNode));
   if (nvlNode == NULL) {
     // NVML NVLink detection
-    int maxNvLinks = (sm < 60) ? 0 : (sm < 70) ? 4 : (sm < 80) ? 6 : 12;
+    int maxNvLinks = (sm < 60) ? 0 : (sm < 70) ? 4 : (sm < 80) ? 6 : (sm < 90) ? 12 : 18;
 
     if (maxNvLinks > 0 && nvmlDev == NULL) {
       WARN("No NVML device handle. Skipping nvlink detection.");
@@ -641,8 +641,21 @@ ncclResult_t ncclTopoGetXmlFromGpu(struct ncclXmlNode* pciNode, nvmlDevice_t nvm
       if ((ncclNvmlDeviceGetNvLinkCapability(nvmlDev, l, NVML_NVLINK_CAP_P2P_SUPPORTED, &canP2P) != ncclSuccess) || !canP2P) continue;
 
       // Make sure the Nvlink is up. The previous call should have trained the link.
-      nvmlEnableState_t isActive;
-      if ((ncclNvmlDeviceGetNvLinkState(nvmlDev, l, &isActive) != ncclSuccess) || (isActive != NVML_FEATURE_ENABLED)) continue;
+      nvmlEnableState_t isActive = NVML_FEATURE_DISABLED;
+#if CUDART_VERSION >= 11080
+      if (sm >= 90) {
+        nvmlFieldValue_t fv;
+        fv.fieldId = NVML_FI_DEV_NVLINK_GET_STATE;
+        fv.scopeId = l;
+        // fv.value will contain NV_FEATURE_ENABLED or NV_FEATURE_DISABLED
+        if ((ncclNvmlDeviceGetFieldValues(nvmlDev, 1, &fv) == ncclSuccess) && (fv.nvmlReturn == NVML_SUCCESS))
+          isActive = (nvmlEnableState_t) fv.value.uiVal;
+      } else /* FALLTHRU to GetNvLinkState if before SM90 */
+#endif
+      {
+        (void) ncclNvmlDeviceGetNvLinkState(nvmlDev, l, &isActive);
+      }
+      if (isActive != NVML_FEATURE_ENABLED) continue;
 
       // Try to figure out what's on the other side of the NVLink
       nvmlPciInfo_t remoteProc;
diff --git a/src/group.cc b/src/group.cc
index 590068d..d246f28 100644
--- a/src/group.cc
+++ b/src/group.cc
@@ -211,8 +211,8 @@ static void groupCleanup(struct ncclComm** groupCommHeadPtr, struct ncclComm** g
     for (int i = 0; i < comm->nRanks; i++) {
       comm->tasks.peers[i].sendSeen = false;
       comm->tasks.peers[i].recvSeen = false;
-      comm->connectSend[i] = 0;
-      comm->connectRecv[i] = 0;
+      comm->connectSend[i] = 0UL;
+      comm->connectRecv[i] = 0UL;
     }
     comm->unlaunchedPlansHead = nullptr;
     // Reclaim abandoned kernel plan memory. Note ncclWork structs were already
diff --git a/src/include/comm.h b/src/include/comm.h
index 2adce32..16e95b3 100644
--- a/src/include/comm.h
+++ b/src/include/comm.h
@@ -168,8 +168,8 @@ struct ncclComm {
   ncclCollNet_t* ncclCollNet;
   void* bootstrap;
   // Bitmasks for ncclTransportP2pSetup
-  uint32_t* connectSend;
-  uint32_t* connectRecv;
+  uint64_t* connectSend;
+  uint64_t* connectRecv;
 
   int rank;    // my rank in the communicator
   int nRanks;  // number of GPUs in communicator
diff --git a/src/include/cudawrap.h b/src/include/cudawrap.h
index 2bd3b4d..0fd5945 100644
--- a/src/include/cudawrap.h
+++ b/src/include/cudawrap.h
@@ -8,6 +8,8 @@
 #define NCCL_CUDAWRAP_H_
 
 #include <cuda.h>
+#include <cuda_runtime.h>
+#include "checks.h"
 
 #if CUDART_VERSION >= 11030
 #include <cudaTypedefs.h>
@@ -83,6 +85,18 @@ DECLARE_CUDA_PFN_EXTERN(cuDriverGetVersion, 2020);
 DECLARE_CUDA_PFN_EXTERN(cuGetProcAddress, 11030);
 
 
-ncclResult_t cudaLibraryInit(void);
+ncclResult_t ncclCudaLibraryInit(void);
+
+extern int ncclCudaDriverVersionCache;
+
+inline ncclResult_t ncclCudaDriverVersion(int* driver) {
+  int version = __atomic_load_n(&ncclCudaDriverVersionCache, __ATOMIC_RELAXED);
+  if (version == -1) {
+    CUDACHECK(cudaDriverGetVersion(&version));
+    __atomic_store_n(&ncclCudaDriverVersionCache, version, __ATOMIC_RELAXED);
+  }
+  *driver = version;
+  return ncclSuccess;
+}
 
 #endif
diff --git a/src/include/graph.h b/src/include/graph.h
index 63b05b1..26c1e76 100644
--- a/src/include/graph.h
+++ b/src/include/graph.h
@@ -33,6 +33,7 @@ ncclResult_t ncclTopoGetNvbGpus(struct ncclTopoSystem* system, int rank, int* nr
 ncclResult_t ncclTopoGetNetDev(struct ncclComm* comm, int rank, struct ncclTopoGraph* graph, int channelId, int peerRank, int* net, int* proxyRank);
 ncclResult_t ncclTopoCheckP2p(struct ncclTopoSystem* system, int64_t id1, int64_t id2, int* p2p, int *read, int* intermediateRank);
 ncclResult_t ncclTopoCheckGdr(struct ncclTopoSystem* topo, int64_t busId, int netDev, int read, int* useGdr);
+ncclResult_t ncclTopoNeedFlush(struct ncclTopoSystem* system, int64_t busId, int* flush);
 ncclResult_t ncclTopoCheckNet(struct ncclTopoSystem* system, int64_t id1, int64_t id2, int* net);
 int ncclPxnDisable(struct ncclComm* comm);
 ncclResult_t ncclTopoGetPxnRanks(struct ncclComm* comm, int** intermediateRanks, int* nranks);
diff --git a/src/include/nvmlwrap.h b/src/include/nvmlwrap.h
index 29731dd..fa1f5cf 100644
--- a/src/include/nvmlwrap.h
+++ b/src/include/nvmlwrap.h
@@ -107,6 +107,75 @@ typedef enum nvmlGpuP2PCapsIndex_enum
     NVML_P2P_CAPS_INDEX_UNKNOWN
 } nvmlGpuP2PCapsIndex_t;
 
+/**
+ * Represents the type for sample value returned
+ */
+typedef enum nvmlValueType_enum
+{
+    NVML_VALUE_TYPE_DOUBLE = 0,
+    NVML_VALUE_TYPE_UNSIGNED_INT = 1,
+    NVML_VALUE_TYPE_UNSIGNED_LONG = 2,
+    NVML_VALUE_TYPE_UNSIGNED_LONG_LONG = 3,
+    NVML_VALUE_TYPE_SIGNED_LONG_LONG = 4,
+
+    // Keep this last
+    NVML_VALUE_TYPE_COUNT
+}nvmlValueType_t;
+
+
+/**
+ * Union to represent different types of Value
+ */
+typedef union nvmlValue_st
+{
+    double dVal;                    //!< If the value is double
+    unsigned int uiVal;             //!< If the value is unsigned int
+    unsigned long ulVal;            //!< If the value is unsigned long
+    unsigned long long ullVal;      //!< If the value is unsigned long long
+    signed long long sllVal;        //!< If the value is signed long long
+}nvmlValue_t;
+
+/**
+ * Field Identifiers.
+ *
+ * All Identifiers pertain to a device. Each ID is only used once and is guaranteed never to change.
+ */
+
+/* NVLink Speed */
+#define NVML_FI_DEV_NVLINK_SPEED_MBPS_COMMON 90  //!< Common NVLink Speed in MBps for active links
+#define NVML_FI_DEV_NVLINK_LINK_COUNT        91  //!< Number of NVLinks present on the device
+
+/**
+ * Remote device NVLink ID
+ *
+ * Link ID needs to be specified in the scopeId field in nvmlFieldValue_t.
+ */
+#define NVML_FI_DEV_NVLINK_REMOTE_NVLINK_ID     146 //!< Remote device NVLink ID
+
+/**
+ * NVSwitch: connected NVLink count
+ */
+#define NVML_FI_DEV_NVSWITCH_CONNECTED_LINK_COUNT   147  //!< Number of NVLinks connected to NVSwitch
+
+#define NVML_FI_DEV_NVLINK_GET_SPEED                  164
+#define NVML_FI_DEV_NVLINK_GET_STATE                  165
+#define NVML_FI_DEV_NVLINK_GET_VERSION                166
+#define NVML_FI_MAX 167 //!< One greater than the largest field ID defined above
+
+/**
+ * Information for a Field Value Sample
+ */
+typedef struct nvmlFieldValue_st
+{
+    unsigned int fieldId;       //!< ID of the NVML field to retrieve. This must be set before any call that uses this struct. See the constants starting with NVML_FI_ above.
+    unsigned int scopeId;       //!< Scope ID can represent data used by NVML depending on fieldId's context. For example, for NVLink throughput counter data, scopeId can represent linkId.
+    long long timestamp;        //!< CPU Timestamp of this value in microseconds since 1970
+    long long latencyUsec;      //!< How long this field value took to update (in usec) within NVML. This may be averaged across several fields that are serviced by the same driver call.
+    nvmlValueType_t valueType;  //!< Type of the value stored in value
+    nvmlReturn_t nvmlReturn;    //!< Return code for retrieving this value. This must be checked before looking at value, as value is undefined if nvmlReturn != NVML_SUCCESS
+    nvmlValue_t value;          //!< Value for this field. This is only valid if nvmlReturn == NVML_SUCCESS
+} nvmlFieldValue_t;
+
 /* End of nvml.h */
 #endif // NCCL_NVML_DIRECT
 
@@ -135,4 +204,6 @@ ncclResult_t ncclNvmlDeviceGetNvLinkRemotePciInfo(nvmlDevice_t device, unsigned
 ncclResult_t ncclNvmlDeviceGetNvLinkCapability(nvmlDevice_t device, unsigned int link, nvmlNvLinkCapability_t capability, unsigned int *capResult);
 ncclResult_t ncclNvmlDeviceGetCudaComputeCapability(nvmlDevice_t device, int* major, int* minor);
 ncclResult_t ncclNvmlDeviceGetP2PStatus(nvmlDevice_t device1, nvmlDevice_t device2, nvmlGpuP2PCapsIndex_t p2pIndex, nvmlGpuP2PStatus_t* p2pStatus);
+ncclResult_t ncclNvmlDeviceGetFieldValues(nvmlDevice_t device, int valuesCount, nvmlFieldValue_t *values);
+
 #endif // End include guard
diff --git a/src/include/strongstream.h b/src/include/strongstream.h
index b72f77c..74df610 100644
--- a/src/include/strongstream.h
+++ b/src/include/strongstream.h
@@ -22,7 +22,7 @@ struct ncclCudaGraph {
 #endif
 };
 
-inline struct ncclCudaGraph ncclCudaGraphNull() {
+inline struct ncclCudaGraph ncclCudaGraphNone() {
   struct ncclCudaGraph tmp;
   #if CUDART_VERSION >= 11030
     tmp.graph = nullptr;
@@ -50,7 +50,6 @@ inline bool ncclCudaGraphSame(struct ncclCudaGraph a, struct ncclCudaGraph b) {
 ncclResult_t ncclCudaGetCapturingGraph(struct ncclCudaGraph* graph, cudaStream_t stream);
 ncclResult_t ncclCudaGraphAddDestructor(struct ncclCudaGraph graph, cudaHostFn_t fn, void* arg);
 
-
 /* ncclStrongStream: An abstraction over CUDA streams that do not lose their
  * identity while being captured. Regular streams have the deficiency that the
  * captured form of a stream in one graph launch has no relation to the
@@ -88,7 +87,7 @@ ncclResult_t ncclStrongStreamAcquire(
 // Acquire-fence the strong stream assuming no graph is capturing. This permits
 // the caller to enqueue directly to the `ss->stream` member using native CUDA
 // calls. Strong stream must be released via:
-//   ncclStrongStreamRelease(ncclCudaGraphNull(), graphRefs, ss);
+//   ncclStrongStreamRelease(ncclCudaGraphNone(), ss);
 ncclResult_t ncclStrongStreamAcquireUncaptured(struct ncclStrongStream* ss);
 
 // Release-fence of the strong stream.
diff --git a/src/init.cc b/src/init.cc
index 8023c49..397946e 100644
--- a/src/init.cc
+++ b/src/init.cc
@@ -416,7 +416,7 @@ static ncclResult_t devCommSetup(ncclComm_t comm) {
 
   NCCLCHECK(ncclCudaMemcpyAsync(devCommAndChans, &tmpCommAndChans, 1, comm->deviceStream.stream));
   CUDACHECK(cudaStreamSynchronize(comm->deviceStream.stream));
-  NCCLCHECK(ncclStrongStreamRelease(ncclCudaGraphNull(), &comm->deviceStream));
+  NCCLCHECK(ncclStrongStreamRelease(ncclCudaGraphNone(), &comm->deviceStream));
   return ncclSuccess;
 }
 
@@ -955,13 +955,13 @@ collnet_cleanup:
       for (int c=0; c<comm->p2pnChannelsPerPeer; c++) {
         NCCLCHECK(ncclChannelCompute(comm, peer, c, ncclFuncSend, &channelId));
         if (comm->channels[channelId].peers[peer].send[1].connected == 0) {
-          comm->connectSend[peer] |= (1<<channelId);
+          comm->connectSend[peer] |= (1UL<<channelId);
         }
       }
       for (int c=0; c<comm->p2pnChannelsPerPeer; c++) {
         NCCLCHECK(ncclChannelCompute(comm, peer, c, ncclFuncRecv, &channelId));
         if (comm->channels[channelId].peers[peer].recv[1].connected == 0) {
-          comm->connectRecv[peer] |= (1<<channelId);
+          comm->connectRecv[peer] |= (1UL<<channelId);
         }
       }
     }
@@ -1172,7 +1172,7 @@ ncclResult_t ncclCommInitRank(ncclComm_t* newcomm, int nranks, ncclUniqueId comm
   NVTX3_FUNC_RANGE_IN(nccl_domain);
 
   // Load the CUDA driver and dlsym hooks (can fail on old drivers)
-  (void) cudaLibraryInit();
+  (void)ncclCudaLibraryInit();
 
   int cudaDev;
   CUDACHECK(cudaGetDevice(&cudaDev));
@@ -1187,7 +1187,7 @@ ncclResult_t ncclCommInitAll(ncclComm_t* comms, int ndev, const int* devlist) {
   int totalnDev;
   int *gpuFlags = NULL;
   // Load the CUDA driver and dlsym hooks (can fail on old drivers)
-  (void) cudaLibraryInit();
+  (void)ncclCudaLibraryInit();
 
   NCCLCHECKGOTO(PtrCheck(comms, "CommInitAll", "comms"), ret, fail);
   if (ndev < 0) {
@@ -1279,7 +1279,7 @@ ncclResult_t ncclCommInitRankConfig(ncclComm_t *newcomm, int nranks, ncclUniqueI
   }
   if (blockingEnv == 1) internalConfigPtr->blocking = blockingEnv;
 
-  (void) cudaLibraryInit();
+  (void)ncclCudaLibraryInit();
   CUDACHECKGOTO(cudaGetDevice(&cudaDev), ret, exit);
   NCCLCHECKGOTO(ncclCommInitRankDev(newcomm, nranks, commId, myrank, cudaDev, internalConfigPtr), ret, fail);
 
diff --git a/src/misc/cudawrap.cc b/src/misc/cudawrap.cc
index 52663b5..b1786f4 100644
--- a/src/misc/cudawrap.cc
+++ b/src/misc/cudawrap.cc
@@ -38,7 +38,7 @@ DECLARE_CUDA_PFN(cuGetProcAddress, 11030);
 #define CUDA_DRIVER_MIN_VERSION 11030
 
 static void *cudaLib;
-static int cudaDriverVersion;
+int ncclCudaDriverVersionCache = -1;
 
 #if CUDART_VERSION >= 11030
 /*
@@ -107,16 +107,17 @@ static void initOnceFunc() {
     goto error;
   }
 
-  res = pfn_cuDriverGetVersion(&cudaDriverVersion);
+  int driverVersion;
+  res = pfn_cuDriverGetVersion(&driverVersion);
   if (res != 0) {
     WARN("cuDriverGetVersion failed with %d", res);
     goto error;
   }
 
-  INFO(NCCL_INIT, "cudaDriverVersion %d", cudaDriverVersion);
+  INFO(NCCL_INIT, "cudaDriverVersion %d", driverVersion);
 
-  if (cudaDriverVersion < CUDA_DRIVER_MIN_VERSION) {
-    // WARN("CUDA Driver version found is %d. Minimum requirement is %d", cudaDriverVersion, CUDA_DRIVER_MIN_VERSION);
+  if (driverVersion < CUDA_DRIVER_MIN_VERSION) {
+    // WARN("CUDA Driver version found is %d. Minimum requirement is %d", driverVersion, CUDA_DRIVER_MIN_VERSION);
     // Silently ignore version check mismatch for backwards compatibility
     goto error;
   }
@@ -148,7 +149,7 @@ error:
   return;
 }
 
-ncclResult_t cudaLibraryInit() {
+ncclResult_t ncclCudaLibraryInit() {
   pthread_once(&initOnceControl, initOnceFunc);
   return initResult;
 }
diff --git a/src/misc/nvmlwrap.cc b/src/misc/nvmlwrap.cc
index 5db7c6b..2de993a 100644
--- a/src/misc/nvmlwrap.cc
+++ b/src/misc/nvmlwrap.cc
@@ -38,6 +38,7 @@ namespace {
   NCCL_NVML_FN(nvmlDeviceGetNvLinkCapability, nvmlReturn_t, (nvmlDevice_t device, unsigned int link, nvmlNvLinkCapability_t capability, unsigned int *capResult))
   NCCL_NVML_FN(nvmlDeviceGetCudaComputeCapability, nvmlReturn_t, (nvmlDevice_t device, int* major, int* minor))
   NCCL_NVML_FN(nvmlDeviceGetP2PStatus, nvmlReturn_t, (nvmlDevice_t device1, nvmlDevice_t device2, nvmlGpuP2PCapsIndex_t p2pIndex, nvmlGpuP2PStatus_t* p2pStatus))
+  NCCL_NVML_FN(nvmlDeviceGetFieldValues, nvmlReturn_t, (nvmlDevice_t device, int valuesCount, nvmlFieldValue_t *values))
 
   std::mutex lock; // NVML has had some thread safety bugs
   bool initialized = false;
@@ -80,7 +81,8 @@ ncclResult_t ncclNvmlEnsureInitialized() {
       {(void**)&pfn_nvmlDeviceGetNvLinkRemotePciInfo, "nvmlDeviceGetNvLinkRemotePciInfo"},
       {(void**)&pfn_nvmlDeviceGetNvLinkCapability, "nvmlDeviceGetNvLinkCapability"},
       {(void**)&pfn_nvmlDeviceGetCudaComputeCapability, "nvmlDeviceGetCudaComputeCapability"},
-      {(void**)&pfn_nvmlDeviceGetP2PStatus, "nvmlDeviceGetP2PStatus"}
+      {(void**)&pfn_nvmlDeviceGetP2PStatus, "nvmlDeviceGetP2PStatus"},
+      {(void**)&pfn_nvmlDeviceGetFieldValues, "nvmlDeviceGetFieldValues"}
     };
     for(Symbol sym: symbols) {
       *sym.ppfn = dlsym(libhandle, sym.name);
@@ -260,3 +262,10 @@ ncclResult_t ncclNvmlDeviceGetP2PStatus(
   }
   return ncclSuccess;
 }
+
+ncclResult_t ncclNvmlDeviceGetFieldValues(nvmlDevice_t device, int valuesCount, nvmlFieldValue_t *values) {
+  NCCLCHECK(ncclNvmlEnsureInitialized());
+  std::lock_guard<std::mutex> locked(lock);
+  NVMLTRY(nvmlDeviceGetFieldValues, device, valuesCount, values);
+  return ncclSuccess;
+}
diff --git a/src/misc/strongstream.cc b/src/misc/strongstream.cc
index 4933799..0524223 100644
--- a/src/misc/strongstream.cc
+++ b/src/misc/strongstream.cc
@@ -5,6 +5,7 @@
  ************************************************************************/
 
 #include "strongstream.h"
+#include "cudawrap.h"
 #include "checks.h"
 #include "param.h"
 
@@ -14,10 +15,8 @@ ncclResult_t ncclCudaGetCapturingGraph(
     struct ncclCudaGraph* graph, cudaStream_t stream
   ) {
   #if CUDART_VERSION >= 11030
-    thread_local int driver = -1;
-    if (driver == -1) {
-      CUDACHECK(cudaDriverGetVersion(&driver));
-    }
+    int driver;
+    NCCLCHECK(ncclCudaDriverVersion(&driver));
     if (driver < 11030) {
       cudaStreamCaptureStatus status;
       unsigned long long gid;
@@ -192,11 +191,11 @@ ncclResult_t ncclStrongStreamWaitStream(
         CUDACHECK(cudaEventRecord(b->event, b->stream));
       }
       CUDACHECK(cudaStreamWaitEvent(a->stream, b->event, 0));
-      a->eventIsLagging = 1;
     } else {
       cudaGraphNode_t pair[2] = {a->node, b->node};
       CUDACHECK(cudaGraphAddEmptyNode(&a->node, graph.graph, pair, 2));
     }
+    a->eventIsLagging = 1;
   #else
     CUDACHECK(cudaEventRecord(b->event, b->stream));
     CUDACHECK(cudaStreamWaitEvent(a->stream, b->event, 0));
@@ -232,9 +231,8 @@ ncclResult_t ncclStrongStreamWaitStream(
         }
         cudaGraphNode_t pair[2] = {a->node, tie};
         CUDACHECK(cudaGraphAddEmptyNode(&a->node, graph.graph, pair, 2));
+        a->eventIsLagging = 1;
       }
-      // a->eventIsLagging doesn't change since we are just updating the
-      // dependencies of a->node.
     }
   #else
     CUDACHECK(cudaEventRecord(a->event, b));
diff --git a/src/proxy.cc b/src/proxy.cc
index 1a2f361..696f57f 100644
--- a/src/proxy.cc
+++ b/src/proxy.cc
@@ -1055,8 +1055,8 @@ void* ncclProxyService(void* _args) {
   int asyncOpCount = 0;
   while ((stop == 0 || (stop == 1 && npeers > 0)) && *comm->abortFlag == 0) {
     /* never let proxy service thread blocks in poll, or it cannot receive abortFlag. */
-    if (int error = poll(pollfds, NCCL_MAX_LOCAL_RANKS+1, asyncOpCount ? 0 : 500) < 0) {
-      WARN("[Proxy Service] Poll failed with error %d", error);
+    if (poll(pollfds, NCCL_MAX_LOCAL_RANKS+1, asyncOpCount ? 0 : 500) < 0) {
+      WARN("[Proxy Service] Poll failed: %s\n", strerror(errno));
       return NULL;
     }
     if (pollfds[NCCL_MAX_LOCAL_RANKS].revents) {
diff --git a/src/transport.cc b/src/transport.cc
index 7ebaf27..b3ca90d 100644
--- a/src/transport.cc
+++ b/src/transport.cc
@@ -42,7 +42,7 @@ static ncclResult_t selectTransport(struct ncclComm* comm, struct ncclTopoGraph*
 ncclResult_t ncclTransportP2pConnect(struct ncclComm* comm, int channelId, int nrecv, int* peerRecv, int nsend, int* peerSend, int connIndex) {
   TRACE(NCCL_INIT, "nsend %d nrecv %d", nsend, nrecv);
   struct ncclChannel* channel = &comm->channels[channelId];
-  uint32_t mask = 1 << channelId;
+  uint64_t mask = 1UL << channel->id;
   for (int i=0; i<nrecv; i++) {
     int peer = peerRecv[i];
     if (peer == -1 || peer >= comm->nRanks || peer == comm->rank || channel->peers[peer].recv[connIndex].connected) continue;
@@ -77,15 +77,15 @@ ncclResult_t ncclTransportP2pSetup(struct ncclComm* comm, struct ncclTopoGraph*
     int bootstrapTag = (i<<8) + (graph ? graph->id+1 : 0);
     int recvPeer = (comm->rank - i + comm->nRanks) % comm->nRanks;
     int sendPeer = (comm->rank + i) % comm->nRanks;
-    uint32_t recvMask = comm->connectRecv[recvPeer];
-    uint32_t sendMask = comm->connectSend[sendPeer];
+    uint64_t recvMask = comm->connectRecv[recvPeer];
+    uint64_t sendMask = comm->connectSend[sendPeer];
 
     struct ncclConnect* recvData = data;
     int sendChannels = 0, recvChannels = 0;
     int type;
     TIME_START(0);
     for (int c=0; c<MAXCHANNELS; c++) {
-      if (recvMask & (1<<c)) {
+      if (recvMask & (1UL<<c)) {
         NCCLCHECK(selectTransport<0>(comm, graph, recvData+recvChannels++, c, recvPeer, connIndex, &type));
         if (type > highestType) highestType = type;
       }
@@ -94,7 +94,7 @@ ncclResult_t ncclTransportP2pSetup(struct ncclComm* comm, struct ncclTopoGraph*
     TIME_START(1);
     struct ncclConnect* sendData = recvData+recvChannels;
     for (int c=0; c<MAXCHANNELS; c++) {
-      if (sendMask & (1<<c)) {
+      if (sendMask & (1UL<<c)) {
         NCCLCHECK(selectTransport<1>(comm, graph, sendData+sendChannels++, c, sendPeer, connIndex, &type));
         if (type > highestType) highestType = type;
       }
@@ -119,7 +119,7 @@ ncclResult_t ncclTransportP2pSetup(struct ncclComm* comm, struct ncclTopoGraph*
 
     TIME_START(3);
     for (int c=0; c<MAXCHANNELS; c++) {
-      if (sendMask & (1<<c)) {
+      if (sendMask & (1UL<<c)) {
         struct ncclConnector* conn = comm->channels[c].peers[sendPeer].send + connIndex;
         NCCLCHECK(conn->transportComm->connect(comm, sendData++, 1, comm->rank, conn));
         conn->connected = 1;
@@ -129,7 +129,7 @@ ncclResult_t ncclTransportP2pSetup(struct ncclComm* comm, struct ncclTopoGraph*
     TIME_STOP(3);
     TIME_START(4);
     for (int c=0; c<MAXCHANNELS; c++) {
-      if (recvMask & (1<<c)) {
+      if (recvMask & (1UL<<c)) {
         struct ncclConnector* conn = comm->channels[c].peers[recvPeer].recv + connIndex;
         NCCLCHECK(conn->transportComm->connect(comm, recvData++, 1, comm->rank, conn));
         conn->connected = 1;
@@ -137,7 +137,7 @@ ncclResult_t ncclTransportP2pSetup(struct ncclComm* comm, struct ncclTopoGraph*
       }
     }
     TIME_STOP(4);
-    comm->connectRecv[recvPeer] = comm->connectSend[sendPeer] = 0;
+    comm->connectRecv[recvPeer] = comm->connectSend[sendPeer] = 0UL;
   }
   CUDACHECK(cudaStreamSynchronize(transportSetupStream));
   CUDACHECK(cudaStreamDestroy(transportSetupStream));
diff --git a/src/transport/coll_net.cc b/src/transport/coll_net.cc
index 432511c..de10f2f 100644
--- a/src/transport/coll_net.cc
+++ b/src/transport/coll_net.cc
@@ -121,6 +121,7 @@ struct recvResources {
   int netDev;
   int useGdr;
   int useDmaBuf;
+  int needFlush;
   uint64_t* gdcSync;
   uint64_t* gdcFlush;
   void* gdrDesc;
@@ -139,6 +140,7 @@ static ncclResult_t canConnect(int* ret, struct ncclTopoSystem* topo, struct ncc
 struct setupReq {
   int netDev;
   int useGdr;
+  int needFlush;
 };
 
 
@@ -151,6 +153,8 @@ static ncclResult_t sendSetup(struct ncclComm* comm, struct ncclTopoGraph* graph
   NCCLCHECK(ncclTopoGetNetDev(comm, myInfo->rank, graph, channelId, -1, &req.netDev, &proxyRank));
   NCCLCHECK(ncclTopoCheckGdr(comm->topo, myInfo->busId, req.netDev, 1, &req.useGdr));
   send->conn.direct |= req.useGdr ? NCCL_DIRECT_NIC : 0;
+  // Determine whether we need to flush the GDR buffer on recv or not
+  if (req.useGdr) NCCLCHECK(ncclTopoNeedFlush(comm->topo, myInfo->busId, &req.needFlush));
 
   NCCLCHECK(ncclTopoGetLocalRank(comm->topo, myInfo->rank, &send->proxyConn.localRank));
   NCCLCHECK(ncclProxyConnect(comm, TRANSPORT_COLLNET, 1, myInfo->rank, &send->proxyConn));
@@ -392,6 +396,7 @@ static ncclResult_t recvProxySetup(struct ncclProxyConnection* connection, struc
 
   resources->netDev = req->netDev;
   resources->useGdr = req->useGdr;
+  resources->needFlush = req->needFlush;
   ncclNetProperties_t props;
   NCCLCHECK(collNetGetProperties(comm, req->netDev, &props));
   /* DMA-BUF support */
@@ -754,7 +759,7 @@ static ncclResult_t recvProxyProgress(struct ncclComm* comm, struct ncclProxyArg
           TRACE(NCCL_NET, "recvProxy [%d/%d/%d] received, size %d", sub->received, group, buffSlot, totalSize);
           sub->received += args->sliceSteps;
           sub->requests[buffSlot] = NULL;
-          if (1 && reqFifo[group][buffSlot].size > 0 && resources->useGdr) {
+          if (reqFifo[group][buffSlot].size > 0 && resources->useGdr && resources->needFlush) {
             // GDRCOPY support
             if (resources->gdcFlush) {
 #if defined (__x86_64__)
diff --git a/src/transport/net.cc b/src/transport/net.cc
index 12390c0..a3a1579 100644
--- a/src/transport/net.cc
+++ b/src/transport/net.cc
@@ -118,6 +118,7 @@ struct recvResources {
   int netDev;
   int useGdr;
   int useDmaBuf;
+  int needFlush;
   int maxRecvs;
   uint64_t* gdcSync;
   uint64_t* gdcFlush;
@@ -152,6 +153,7 @@ struct setupReq {
   int shared;
   int netDev;
   int useGdr;
+  int needFlush;
   int channelId;
   int connIndex;
 };
@@ -205,6 +207,9 @@ static ncclResult_t recvSetup(struct ncclComm* comm, struct ncclTopoGraph* graph
   NCCLCHECK(ncclTopoGetNetDev(comm, myInfo->rank, graph, channelId, myInfo->rank, &req.netDev, &proxyRank));
   NCCLCHECK(ncclTopoCheckGdr(comm->topo, myInfo->busId, req.netDev, 0, &req.useGdr));
 
+  // Determine whether we need to flush the GDR buffer on recv or not
+  if (req.useGdr) NCCLCHECK(ncclTopoNeedFlush(comm->topo, myInfo->busId, &req.needFlush));
+
   // We don't support PXN on receive yet
   NCCLCHECK(ncclProxyConnect(comm, TRANSPORT_NET, 0, myInfo->rank, &recv->proxyConn));
 
@@ -470,6 +475,7 @@ static ncclResult_t recvProxySetup(struct ncclProxyConnection* connection, struc
   resources->netDev = req->netDev;
   resources->shared = connection->shared = req->shared;
   resources->useGdr = req->useGdr;
+  resources->needFlush = req->needFlush;
   resources->channelId = req->channelId;
   resources->connIndex = req->connIndex;
   ncclNetProperties_t props;
@@ -1033,7 +1039,7 @@ static ncclResult_t recvProxyProgress(struct ncclComm* comm, struct ncclProxyArg
         for (int i=0; i<NCCL_PROXY_MAX_SUBS; i++) sizes[i] = 0;
         NCCLCHECK(ncclNetTest(comm, subGroup->requests[step%NCCL_STEPS], &done, sizes));
         if (done) {
-          int useGdr = 0;
+          int needFlush = 0;
           int totalSize = 0;
           for (int i=0; i<NCCL_PROXY_MAX_SUBS; i++) totalSize += sizes[i];
           for (int i=0; i<subGroup->groupSize; i++) {
@@ -1042,11 +1048,11 @@ static ncclResult_t recvProxyProgress(struct ncclComm* comm, struct ncclProxyArg
             for (uint64_t step=sub->received-args->sliceSteps; step<sub->received; step++) ncclProfilingRecord(args, s+i, step, ncclProxyProfileRecvFlushWait);
             if (step < sub->nsteps) {
               struct recvResources* resources = (struct recvResources*) (sub->connection->transportResources);
-              if (resources->useGdr) useGdr = 1;
+              if (resources->useGdr) needFlush |= resources->needFlush;
             }
           }
           subGroup->requests[step%NCCL_STEPS] = NULL;
-          if (totalSize > 0 && p == NCCL_PROTO_SIMPLE && useGdr) {
+          if (totalSize > 0 && p == NCCL_PROTO_SIMPLE && needFlush) {
             // GDRCOPY support
             struct recvResources* resources = (struct recvResources*) (subGroup->connection->transportResources);
             if (resources->gdcFlush) {