[PATCH][4/26] IB/mthca: improve CQ locking part 2

[Roland Dreier]

From: Michael S. Tsirkin <mst@xxxxxxxxxxxxxx>

Locking during the poll cq operation can be reduced by locking the cq
while qp is being removed from the qp array.  This also avoids an
extra atomic operation for reference counting.

Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxxxxxx>
Signed-off-by: Roland Dreier <roland@xxxxxxxxxxx>


--- linux-export.orig/drivers/infiniband/hw/mthca/mthca_cq.c	2005-03-03 14:12:52.368554099 -0800
+++ linux-export/drivers/infiniband/hw/mthca/mthca_cq.c	2005-03-03 14:12:52.923433653 -0800
@@ -418,14 +418,14 @@
 			spin_unlock(&(*cur_qp)->lock);
 		}
 
-		spin_lock(&dev->qp_table.lock);
+		/*
+		 * We do not have to take the QP table lock here,
+		 * because CQs will be locked while QPs are removed
+		 * from the table.
+		 */
 		*cur_qp = mthca_array_get(&dev->qp_table.qp,
 					  be32_to_cpu(cqe->my_qpn) &
 					  (dev->limits.num_qps - 1));
-		if (*cur_qp)
-			atomic_inc(&(*cur_qp)->refcount);
-		spin_unlock(&dev->qp_table.lock);
-
 		if (!*cur_qp) {
 			mthca_warn(dev, "CQ entry for unknown QP %06x\n",
 				   be32_to_cpu(cqe->my_qpn) & 0xffffff);
@@ -537,12 +537,8 @@
 		inc_cons_index(dev, cq, freed);
 	}
 
-	if (qp) {
+	if (qp)
 		spin_unlock(&qp->lock);
-		if (atomic_dec_and_test(&qp->refcount))
-			wake_up(&qp->wait);
-	}
-
 
 	spin_unlock_irqrestore(&cq->lock, flags);
 
--- linux-export.orig/drivers/infiniband/hw/mthca/mthca_qp.c	2005-02-03 16:59:28.000000000 -0800
+++ linux-export/drivers/infiniband/hw/mthca/mthca_qp.c	2005-03-03 14:12:52.924433436 -0800
@@ -1083,9 +1083,21 @@
 	return 0;
 
  err_out_free:
-	spin_lock_irq(&dev->qp_table.lock);
+	/*
+	 * Lock CQs here, so that CQ polling code can do QP lookup
+	 * without taking a lock.
+	 */
+	spin_lock_irq(&send_cq->lock);
+	if (send_cq != recv_cq)
+		spin_lock(&recv_cq->lock);
+
+	spin_lock(&dev->qp_table.lock);
 	mthca_array_clear(&dev->qp_table.qp, mqpn);
-	spin_unlock_irq(&dev->qp_table.lock);
+	spin_unlock(&dev->qp_table.lock);
+
+	if (send_cq != recv_cq)
+		spin_unlock(&recv_cq->lock);
+	spin_unlock_irq(&send_cq->lock);
 
  err_out:
 	dma_free_coherent(&dev->pdev->dev, sqp->header_buf_size,
@@ -1100,11 +1112,28 @@
 	u8 status;
 	int size;
 	int i;
+	struct mthca_cq *send_cq;
+	struct mthca_cq *recv_cq;
+
+	send_cq = to_mcq(qp->ibqp.send_cq);
+	recv_cq = to_mcq(qp->ibqp.recv_cq);
 
-	spin_lock_irq(&dev->qp_table.lock);
+	/*
+	 * Lock CQs here, so that CQ polling code can do QP lookup
+	 * without taking a lock.
+	 */
+	spin_lock_irq(&send_cq->lock);
+	if (send_cq != recv_cq)
+		spin_lock(&recv_cq->lock);
+
+	spin_lock(&dev->qp_table.lock);
 	mthca_array_clear(&dev->qp_table.qp,
 			  qp->qpn & (dev->limits.num_qps - 1));
-	spin_unlock_irq(&dev->qp_table.lock);
+	spin_unlock(&dev->qp_table.lock);
+
+	if (send_cq != recv_cq)
+		spin_unlock(&recv_cq->lock);
+	spin_unlock_irq(&send_cq->lock);
 
 	atomic_dec(&qp->refcount);
 	wait_event(qp->wait, !atomic_read(&qp->refcount));

-
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