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Commit 48947109 authored by Mike Marciniszyn's avatar Mike Marciniszyn Committed by Roland Dreier
Browse files

IB/qib: Optimize locking for get_txreq() 



The current code locks the QP s_lock, followed by the pending_lock, I
guess to to protect against the allocate failing.

This patch only locks the pending_lock, assuming that the empty case
is an exeception, in which case the pending_lock is dropped, and the
original code is executed.  This will save a lock of s_lock in the
normal case.

The observation is that the sdma descriptors will deplete at twice the
rate of txreq's, so this should be rare.

Signed-off-by: default avatarMike Marciniszyn <mike.marciniszyn@qlogic.com>
Signed-off-by: default avatarRoland Dreier <roland@purestorage.com>
parent eddfb675

drivers/infiniband/hw/qib/qib_verbs.c

+33 −10
Original line number Diff line number Diff line
@@ -913,8 +913,8 @@ static void copy_io(u32 __iomem *piobuf, struct qib_sge_state *ss, 
		__raw_writel(last, piobuf);

}



static struct qib_verbs_txreq *get_txreq(struct qib_ibdev *dev,

					 struct qib_qp *qp, int *retp)

static noinline struct qib_verbs_txreq *__get_txreq(struct qib_ibdev *dev,

					   struct qib_qp *qp)

{

	struct qib_verbs_txreq *tx;

	unsigned long flags;
@@ -926,8 +926,9 @@ static struct qib_verbs_txreq *get_txreq(struct qib_ibdev *dev, 
		struct list_head *l = dev->txreq_free.next;



		list_del(l);

		spin_unlock(&dev->pending_lock);

		spin_unlock_irqrestore(&qp->s_lock, flags);

		tx = list_entry(l, struct qib_verbs_txreq, txreq.list);

		*retp = 0;

	} else {

		if (ib_qib_state_ops[qp->state] & QIB_PROCESS_RECV_OK &&

		    list_empty(&qp->iowait)) {
@@ -935,14 +936,33 @@ static struct qib_verbs_txreq *get_txreq(struct qib_ibdev *dev, 
			qp->s_flags |= QIB_S_WAIT_TX;

			list_add_tail(&qp->iowait, &dev->txwait);

		}

		tx = NULL;

		qp->s_flags &= ~QIB_S_BUSY;

		*retp = -EBUSY;

	}



		spin_unlock(&dev->pending_lock);

		spin_unlock_irqrestore(&qp->s_lock, flags);

		tx = ERR_PTR(-EBUSY);

	}

	return tx;

}



static inline struct qib_verbs_txreq *get_txreq(struct qib_ibdev *dev,

					 struct qib_qp *qp)

{

	struct qib_verbs_txreq *tx;

	unsigned long flags;



	spin_lock_irqsave(&dev->pending_lock, flags);

	/* assume the list non empty */

	if (likely(!list_empty(&dev->txreq_free))) {

		struct list_head *l = dev->txreq_free.next;



		list_del(l);

		spin_unlock_irqrestore(&dev->pending_lock, flags);

		tx = list_entry(l, struct qib_verbs_txreq, txreq.list);

	} else {

		/* call slow path to get the extra lock */

		spin_unlock_irqrestore(&dev->pending_lock, flags);

		tx =  __get_txreq(dev, qp);

	}

	return tx;

}
@@ -1122,9 +1142,9 @@ static int qib_verbs_send_dma(struct qib_qp *qp, struct qib_ib_header *hdr, 
		goto bail;

	}



	tx = get_txreq(dev, qp, &ret);

	if (!tx)

		goto bail;

	tx = get_txreq(dev, qp);

	if (IS_ERR(tx))

		goto bail_tx;



	control = dd->f_setpbc_control(ppd, plen, qp->s_srate,

				       be16_to_cpu(hdr->lrh[0]) >> 12);
@@ -1195,6 +1215,9 @@ unaligned: 
	ibp->n_unaligned++;

bail:

	return ret;

bail_tx:

	ret = PTR_ERR(tx);

	goto bail;

}



/*