Fixed a really old bug in Infiniband code: QP's max_send_sge was limited to 1

... while we use up to 2 sges (one for transport header and one for payload) per work request in InfUd and up to InfRcTransport::MAX_TX_SGE_COUNT in InfRc. Mellanox drivers/cards never seem to complain about this and the bug was discovered when porting RAMCloud to an Intel OmniPath HPC cluster.

Author: yilongli

src/InfRcTransport.cc

@@ -750,7 +750,8 @@ InfRcTransport::clientTrySetupQueuePair(IpAddress& address)
  ibPhysicalPort, clientSrq,
  commonTxCq, clientRxCq,
  MAX_TX_QUEUE_DEPTH,
- MAX_SHARED_RX_QUEUE_DEPTH);
+ MAX_SHARED_RX_QUEUE_DEPTH,
+ MAX_TX_SGE_COUNT);
  uint64_t nonce = generateRandom();
  LOG(DEBUG, "starting to connect to %s via local port %d, nonce 0x%lx",
  inet_ntoa(sin->sin_addr), clientPort, nonce);
@@ -845,7 +846,8 @@ InfRcTransport::ServerConnectHandler::handleFileEvent(int events)
  transport->commonTxCq,
  transport->serverRxCq,
  MAX_TX_QUEUE_DEPTH,
- MAX_SHARED_RX_QUEUE_DEPTH);
+ MAX_SHARED_RX_QUEUE_DEPTH,
+ MAX_TX_SGE_COUNT);
  qp->plumb(&incomingQpt);
  qp->setPeerName(incomingQpt.getPeerName());
  LOG(DEBUG, "New queue pair for %s:%u, nonce 0x%lx (total creates "

src/InfUdDriver.cc

@@ -186,12 +186,10 @@ InfUdDriver::InfUdDriver(Context* context, const ServiceLocator *sl)
  throw DriverException(HERE, errno);
  }
 
- qp = infiniband->createQueuePair(localMac ? IBV_QPT_RAW_PACKET
- : IBV_QPT_UD,
- ibPhysicalPort, NULL,
- txcq, rxcq, MAX_TX_QUEUE_DEPTH,
- MAX_RX_QUEUE_DEPTH,
- QKEY);
+ qp = infiniband->createQueuePair(
+ localMac ? IBV_QPT_RAW_PACKET : IBV_QPT_UD,
+ ibPhysicalPort, NULL, txcq, rxcq, MAX_TX_QUEUE_DEPTH,
+ MAX_RX_QUEUE_DEPTH, 2, QKEY);
 
  // Cache these for easier access.
  lid = infiniband->getLid(ibPhysicalPort);

src/Infiniband.cc

@@ -69,10 +69,11 @@ Infiniband::dumpStats()
 Infiniband::QueuePair*
 Infiniband::createQueuePair(ibv_qp_type type, int ibPhysicalPort, ibv_srq *srq,
  ibv_cq *txcq, ibv_cq *rxcq, uint32_t maxSendWr,
- uint32_t maxRecvWr, uint32_t QKey)
+ uint32_t maxRecvWr, uint32_t maxSendSges,
+ uint32_t QKey)
 {
  return new QueuePair(*this, type, ibPhysicalPort, srq, txcq, rxcq,
- maxSendWr, maxRecvWr, QKey);
+ maxSendWr, maxRecvWr, maxSendSges, QKey);
 }
 
 /**
@@ -508,12 +509,15 @@ Infiniband::pollCompletionQueue(ibv_cq *cq, int numEntries, ibv_wc *retWcArray)
  * \param maxRecvWr
  * Maximum number of outstanding receive work requests allowed on
  * this QueuePair.
+ * \param maxSendSges
+ * Maximum number of scatter-gather entries per work request allowed on
+ * this QueuePair.
  * \param QKey
  * UD Queue Pairs only. The QKey for this pair. 
  */
 Infiniband::QueuePair::QueuePair(Infiniband& infiniband, ibv_qp_type type,
  int ibPhysicalPort, ibv_srq *srq, ibv_cq *txcq, ibv_cq *rxcq,
- uint32_t maxSendWr, uint32_t maxRecvWr, uint32_t QKey)
+ uint32_t maxSendWr, uint32_t maxRecvWr, uint32_t maxSendSges, uint32_t QKey)
  : infiniband(infiniband),
  type(type),
  ctxt(infiniband.device.ctxt),
@@ -538,7 +542,7 @@ Infiniband::QueuePair::QueuePair(Infiniband& infiniband, ibv_qp_type type,
  qpia.srq = srq; // use the same shared receive queue
  qpia.cap.max_send_wr = maxSendWr; // max outstanding send requests
  qpia.cap.max_recv_wr = maxRecvWr; // max outstanding recv requests
- qpia.cap.max_send_sge = 1;  // max send scatter-gather elements
+ qpia.cap.max_send_sge = maxSendSges; // max send scatter-gather elements
  qpia.cap.max_recv_sge = 1; // max recv scatter-gather elements
  qpia.cap.max_inline_data = // max bytes of immediate data on send q
  MAX_INLINE_DATA;
@@ -993,13 +997,17 @@ Infiniband::Address::getHandle() const
  return ah;
  }
 
- // Must allocate a new address handle.
- ibv_ah_attr attr;
- attr.dlid = lid;
- attr.src_path_bits = 0;
- attr.is_global = 0;
- attr.sl = 0;
- attr.port_num = downCast<uint8_t>(physicalPort);
+ // Must allocate a new address handle. See also:
+ // https://www.rdmamojo.com/2012/09/22/ibv_create_ah/
+ ibv_ah_attr attr = {
+ .grh = {},
+ .dlid = lid,
+ .sl = 0,
+ .src_path_bits = 0,
+ .static_rate = 0,
+ .is_global = 0,
+ .port_num = downCast<uint8_t>(physicalPort)
+ };
  infiniband.totalAddressHandleAllocCalls += 1;
  uint64_t start = Cycles::rdtsc();
  ah = ibv_create_ah(infiniband.pd.pd, &attr);

src/Infiniband.h

@@ -186,6 +186,7 @@ class Infiniband {
  ibv_cq *rxcq,
  uint32_t maxSendWr,
  uint32_t maxRecvWr,
+ uint32_t maxSendSges,
  uint32_t QKey = 0);
  // exists solely as superclass constructor for MockQueuePair derivative
  explicit QueuePair(Infiniband& infiniband)
@@ -460,6 +461,7 @@ class Infiniband {
  ibv_cq *rxcq,
  uint32_t maxSendWr,
  uint32_t maxRecvWr,
+ uint32_t maxSendSges,
  uint32_t QKey = 0);
 
  int getLid(int port);