[dpdk-dev] [PATCH 2/2] cxgbe: fix unnecessary spinning for a lock with trylock instead

[Rahul Lakkireddy]

CXGBE PMD depends on an alarm to periodically transmit any pending
coalesced packets and hence spins for a lock for each tx queue in the
alarm callback.

A better solution is to try to get a lock whenever possible, instead
of spinning for it.

Signed-off-by: Rahul Lakkireddy <rahul.lakkireddy at chelsio.com>
Signed-off-by: Kumar Sanghvi <kumaras at chelsio.com>
---
 drivers/net/cxgbe/base/adapter.h |  9 +++++++++
 drivers/net/cxgbe/sge.c          | 21 ++++++++++++---------
 2 files changed, 21 insertions(+), 9 deletions(-)

diff --git a/drivers/net/cxgbe/base/adapter.h b/drivers/net/cxgbe/base/adapter.h
index a1e8ef7..a5225c0 100644
--- a/drivers/net/cxgbe/base/adapter.h
+++ b/drivers/net/cxgbe/base/adapter.h
@@ -473,6 +473,15 @@ static inline void t4_os_unlock(rte_spinlock_t *lock)
 }
 
 /**
+ * t4_os_trylock - try to get a lock
+ * @lock: the spinlock
+ */
+static inline int t4_os_trylock(rte_spinlock_t *lock)
+{
+	return rte_spinlock_trylock(lock);
+}
+
+/**
  * t4_os_init_list_head - initialize
  * @head: head of list to initialize [to empty]
  */
diff --git a/drivers/net/cxgbe/sge.c b/drivers/net/cxgbe/sge.c
index aa0c2e5..51449e0 100644
--- a/drivers/net/cxgbe/sge.c
+++ b/drivers/net/cxgbe/sge.c
@@ -808,20 +808,23 @@ static void tx_timer_cb(void *data)
 	struct adapter *adap = (struct adapter *)data;
 	struct sge_eth_txq *txq = &adap->sge.ethtxq[0];
 	int i;
+	unsigned int coal_idx;
 
 	/* monitor any pending tx */
 	for (i = 0; i < adap->sge.max_ethqsets; i++, txq++) {
-		t4_os_lock(&txq->txq_lock);
-		if (txq->q.coalesce.idx) {
-			if (txq->q.coalesce.idx == txq->q.last_coal_idx &&
-			    txq->q.pidx == txq->q.last_pidx) {
-				ship_tx_pkt_coalesce_wr(adap, txq);
-			} else {
-				txq->q.last_coal_idx = txq->q.coalesce.idx;
-				txq->q.last_pidx = txq->q.pidx;
+		if (t4_os_trylock(&txq->txq_lock)) {
+			coal_idx = txq->q.coalesce.idx;
+			if (coal_idx) {
+				if (coal_idx == txq->q.last_coal_idx &&
+				    txq->q.pidx == txq->q.last_pidx) {
+					ship_tx_pkt_coalesce_wr(adap, txq);
+				} else {
+					txq->q.last_coal_idx = coal_idx;
+					txq->q.last_pidx = txq->q.pidx;
+				}
 			}
+			t4_os_unlock(&txq->txq_lock);
 		}
-		t4_os_unlock(&txq->txq_lock);
 	}
 	rte_eal_alarm_set(50, tx_timer_cb, (void *)adap);
 }
-- 
2.5.3