netdev - [PATCH v2 net-next 02/12] net: stmmac: Do not keep rearming the coalesce timer in stmmac

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Message-Id: <3924724c28ec69f410f01f53bd342c7429f3038f.1526474646.git.joabreu@synopsys.com>
Date:   Wed, 16 May 2018 13:50:44 +0100
From:   Jose Abreu <Jose.Abreu@...opsys.com>
To:     netdev@...r.kernel.org
Cc:     Jose Abreu <Jose.Abreu@...opsys.com>,
        "David S. Miller" <davem@...emloft.net>,
        Joao Pinto <Joao.Pinto@...opsys.com>,
        Vitor Soares <Vitor.Soares@...opsys.com>,
        Giuseppe Cavallaro <peppe.cavallaro@...com>,
        Alexandre Torgue <alexandre.torgue@...com>
Subject: [PATCH v2 net-next 02/12] net: stmmac: Do not keep rearming the coalesce timer in stmmac_xmit

This is cutting down performance. Once the timer is armed it should run
after the time expires for the first packet sent and not the last one.

After this change, running iperf, the performance gain is +/- 24%.

Signed-off-by: Jose Abreu <joabreu@...opsys.com>
Cc: David S. Miller <davem@...emloft.net>
Cc: Joao Pinto <jpinto@...opsys.com>
Cc: Vitor Soares <soares@...opsys.com>
Cc: Giuseppe Cavallaro <peppe.cavallaro@...com>
Cc: Alexandre Torgue <alexandre.torgue@...com>
---
 drivers/net/ethernet/stmicro/stmmac/stmmac.h      |    1 +
 drivers/net/ethernet/stmicro/stmmac/stmmac_main.c |    5 ++++-
 2 files changed, 5 insertions(+), 1 deletions(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac.h b/drivers/net/ethernet/stmicro/stmmac/stmmac.h
index 42fc76e..4d425b1 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac.h
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac.h
@@ -105,6 +105,7 @@ struct stmmac_priv {
 	u32 tx_count_frames;
 	u32 tx_coal_frames;
 	u32 tx_coal_timer;
+	bool tx_timer_armed;
 
 	int tx_coalesce;
 	int hwts_tx_en;
diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index d9dbe13..789bc22 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -3158,13 +3158,16 @@ static netdev_tx_t stmmac_xmit(struct sk_buff *skb, struct net_device *dev)
 	 * element in case of no SG.
 	 */
 	priv->tx_count_frames += nfrags + 1;
-	if (likely(priv->tx_coal_frames > priv->tx_count_frames)) {
+	if (likely(priv->tx_coal_frames > priv->tx_count_frames) &&
+	    !priv->tx_timer_armed) {
 		mod_timer(&priv->txtimer,
 			  STMMAC_COAL_TIMER(priv->tx_coal_timer));
+		priv->tx_timer_armed = true;
 	} else {
 		priv->tx_count_frames = 0;
 		stmmac_set_tx_ic(priv, desc);
 		priv->xstats.tx_set_ic_bit++;
+		priv->tx_timer_armed = false;
 	}
 
 	skb_tx_timestamp(skb);
-- 
1.7.1