netdev - [RFC PATCH net-next v2 6/7] net: ravb: Enable SW IRQ Coalescing for GbEth

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Date: Tue,  6 Feb 2024 09:19:08 +0000
From: Paul Barker <paul.barker.ct@...renesas.com>
To: Sergey Shtylyov <s.shtylyov@....ru>,
	"David S . Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>
Cc: Paul Barker <paul.barker.ct@...renesas.com>,
	Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
	Wolfram Sang <wsa+renesas@...g-engineering.com>,
	netdev@...r.kernel.org,
	linux-renesas-soc@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [RFC PATCH net-next v2 6/7] net: ravb: Enable SW IRQ Coalescing for GbEth

Software IRQ Coalescing is required to improve network stack performance
in the RZ/G2L SoC family and the RZ/G3S SoC, i.e. the SoCs which use the
GbEth IP.

For the RZ/G2L, network throughput is comparable before and after this
change. CPU usage during TCP RX testing dropped by 6.5% and during UDP
RX testing dropped by 10%.

For the RZ/G2UL, network throughput is greatly increased by this change
(results obtained with iperf3):
  * TCP TX: 2.9% more throughput
  * TCP RX: 1.1% more throughput
  * UDP TX: similar throughput
  * UDP RX: 41500% more throughput

For the RZ/G3S we see improvements in network throughput similar to the
RZ/G2UL.

The improvement of UDP RX bandwidth for the single core SoCs (RZ/G2UL &
RZ/G3S) is particularly critical.

Signed-off-by: Paul Barker <paul.barker.ct@...renesas.com>
---
 drivers/net/ethernet/renesas/ravb.h      | 1 +
 drivers/net/ethernet/renesas/ravb_main.c | 4 ++++
 2 files changed, 5 insertions(+)

diff --git a/drivers/net/ethernet/renesas/ravb.h b/drivers/net/ethernet/renesas/ravb.h
index 55a7a08aabef..ca7a66759e35 100644
--- a/drivers/net/ethernet/renesas/ravb.h
+++ b/drivers/net/ethernet/renesas/ravb.h
@@ -1078,6 +1078,7 @@ struct ravb_hw_info {
 	unsigned nc_queues:1;		/* AVB-DMAC has RX and TX NC queues */
 	unsigned magic_pkt:1;		/* E-MAC supports magic packet detection */
 	unsigned half_duplex:1;		/* E-MAC supports half duplex mode */
+	unsigned needs_irq_coalesce:1;	/* Requires SW IRQ Coalescing to achieve best performance */
 };
 
 struct ravb_private {
diff --git a/drivers/net/ethernet/renesas/ravb_main.c b/drivers/net/ethernet/renesas/ravb_main.c
index 661fd86899ac..7bb80608f260 100644
--- a/drivers/net/ethernet/renesas/ravb_main.c
+++ b/drivers/net/ethernet/renesas/ravb_main.c
@@ -2639,6 +2639,7 @@ static const struct ravb_hw_info gbeth_hw_info = {
 	.tx_counters = 1,
 	.carrier_counters = 1,
 	.half_duplex = 1,
+	.needs_irq_coalesce = 1,
 };
 
 static const struct of_device_id ravb_match_table[] = {
@@ -2983,6 +2984,9 @@ static int ravb_probe(struct platform_device *pdev)
 	if (info->nc_queues)
 		netif_napi_add(ndev, &priv->napi[RAVB_NC], ravb_poll);
 
+	if (info->needs_irq_coalesce)
+		netdev_sw_irq_coalesce_default_on(ndev);
+
 	/* Network device register */
 	error = register_netdev(ndev);
 	if (error)
-- 
2.39.2