netdev - [net-next RFC v3 6/7] net: ravb: Use NAPI threaded mode on 1-core CPUs with GbEth IP

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Date: Mon, 15 Apr 2024 10:48:03 +0100
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>,
	Niklas Söderlund <niklas.soderlund+renesas@...natech.se>,
	Geert Uytterhoeven <geert+renesas@...der.be>,
	netdev@...r.kernel.org,
	linux-renesas-soc@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [net-next RFC v3 6/7] net: ravb: Use NAPI threaded mode on 1-core CPUs with GbEth IP

NAPI Threaded mode (along with the previously enabled SW IRQ Coalescing)
is required to improve network stack performance for single core SoCs
using the GbEth IP (currently the RZ/G2L SoC family and the RZ/G3S SoC).

This patch gives the following improvements during testing with iperf3.

  * RZ/G2UL:
    * TCP TX: +32% bandwidth (638Mbps -> 841Mbps)
    * TXP RX: +8.8% bandwidth (667Mbps -> 726Mbps)
    * UDP RX: +104% bandwidth (53Mbps -> 108Mbps)

  * RZ/G3S:
    * TCP TX: 29% bandwidth (529Mbps -> 681Mbps)
    * UDP RX: +1290% bandwidth (6.46Mbps -> 90Mbps)

  * RZ/Five:
    * UDP RX: Test no longer crashes (0 -> 20 Mbps)

This patch gives the following reductions in performance in the same
testing:

  * RZ/G2UL:
    * UDP TX: -7.5% bandwidth (594Mbps -> 549Mbps)

  * RZ/G3S:
    * UDP TX: -5% bandwidth (625Mbps -> 594Mbps)

These losses are considered acceptable given the benefits shown above.
If UDP TX bandwidth must be maximised for a particular use case, NAPI
threaded mode can be disabled at runtime via sysfs writes.

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_main.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/renesas/ravb_main.c b/drivers/net/ethernet/renesas/ravb_main.c
index 26b70b996bd3..7434faf0820c 100644
--- a/drivers/net/ethernet/renesas/ravb_main.c
+++ b/drivers/net/ethernet/renesas/ravb_main.c
@@ -2938,8 +2938,11 @@ 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)
+	if (info->needs_irq_coalesce) {
 		netdev_sw_irq_coalesce_default_on(ndev);
+		if (num_present_cpus() == 1)
+			dev_set_threaded(ndev, true);
+	}
 
 	/* Network device register */
 	error = register_netdev(ndev);
-- 
2.39.2