From: Sameeh Jubran <sameehj@amazon.com>
Date: Mon, 3 Jun 2019 17:43:27 +0300
Subject: [PATCH] net: ena: optimise calculations for CQ doorbell
Origin: https://git.kernel.org/linus/d91860989dd4bce582ed6c3647a0d41d6fd895b3
Bug-Debian: https://bugs.debian.org/941291

This patch initially checks if CQ doorbell
is needed before proceeding with the calculations.

Signed-off-by: Igor Chauskin <igorch@amazon.com>
Signed-off-by: Sameeh Jubran <sameehj@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
---
 drivers/net/ethernet/amazon/ena/ena_eth_com.h | 20 ++++++++++---------
 1 file changed, 11 insertions(+), 9 deletions(-)

diff --git a/drivers/net/ethernet/amazon/ena/ena_eth_com.h b/drivers/net/ethernet/amazon/ena/ena_eth_com.h
index 0a3d9180e40e..77986c0ea52c 100644
--- a/drivers/net/ethernet/amazon/ena/ena_eth_com.h
+++ b/drivers/net/ethernet/amazon/ena/ena_eth_com.h
@@ -195,15 +195,17 @@ static inline int ena_com_update_dev_comp_head(struct ena_com_io_cq *io_cq)
 	u16 unreported_comp, head;
 	bool need_update;
 
-	head = io_cq->head;
-	unreported_comp = head - io_cq->last_head_update;
-	need_update = unreported_comp > (io_cq->q_depth / ENA_COMP_HEAD_THRESH);
-
-	if (io_cq->cq_head_db_reg && need_update) {
-		pr_debug("Write completion queue doorbell for queue %d: head: %d\n",
-			 io_cq->qid, head);
-		writel(head, io_cq->cq_head_db_reg);
-		io_cq->last_head_update = head;
+	if (unlikely(io_cq->cq_head_db_reg)) {
+		head = io_cq->head;
+		unreported_comp = head - io_cq->last_head_update;
+		need_update = unreported_comp > (io_cq->q_depth / ENA_COMP_HEAD_THRESH);
+
+		if (unlikely(need_update)) {
+			pr_debug("Write completion queue doorbell for queue %d: head: %d\n",
+				 io_cq->qid, head);
+			writel(head, io_cq->cq_head_db_reg);
+			io_cq->last_head_update = head;
+		}
 	}
 
 	return 0;
-- 
2.17.1

