netdev - [PATCH net] r8169: disable TSO on a single version of RTL8168c to fix performance

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Date:   Tue, 19 Nov 2019 10:09:39 +0100
From:   Corinna Vinschen <vinschen@...hat.com>
To:     netdev@...r.kernel.org
Cc:     Heiner Kallweit <hkallweit1@...il.com>, nic_swsd@...ltek.com,
        David Miller <davem@...emloft.net>
Subject: [PATCH net] r8169: disable TSO on a single version of RTL8168c to fix performance

During performance testing, I found that one of my r8169 NICs suffered
a major performance loss, a 8168c model.

Running netperf's TCP_STREAM test didn't return the expected
throughput of > 900 Mb/s, but rather only about 22 Mb/s.  Strange
enough, running the TCP_MAERTS and UDP_STREAM tests all returned with
throughput > 900 Mb/s, as did TCP_STREAM with the other r8169 NICs I can
test (either one of 8169s, 8168e, 8168f).

Bisecting turned up commit 93681cd7d94f83903cb3f0f95433d10c28a7e9a5,
"r8169: enable HW csum and TSO" as the culprit.

I added my 8168c version, RTL_GIGA_MAC_VER_22, to the code
special-casing the 8168evl as per the patch below.  This fixed the
performance problem for me.

Fixes: 93681cd7d94f ("r8169: enable HW csum and TSO")
Signed-off-by: Corinna Vinschen <vinschen@...hat.com>
---
 drivers/net/ethernet/realtek/r8169_main.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/realtek/r8169_main.c b/drivers/net/ethernet/realtek/r8169_main.c
index d8fcdb9db8d1..1de11ac05bd6 100644
--- a/drivers/net/ethernet/realtek/r8169_main.c
+++ b/drivers/net/ethernet/realtek/r8169_main.c
@@ -6952,8 +6952,11 @@ static int rtl_init_one(struct pci_dev *pdev, const struct pci_device_id *ent)
 		dev->gso_max_segs = RTL_GSO_MAX_SEGS_V1;
 	}

-	/* RTL8168e-vl has a HW issue with TSO */
-	if (tp->mac_version == RTL_GIGA_MAC_VER_34) {
+	/* RTL8168e-vl and one RTL8168c variant are known to have a
+	 * HW issue with TSO.
+	 */
+	if (tp->mac_version == RTL_GIGA_MAC_VER_34 ||
+	    tp->mac_version == RTL_GIGA_MAC_VER_22) {
 		dev->vlan_features &= ~(NETIF_F_ALL_TSO | NETIF_F_SG);
 		dev->hw_features &= ~(NETIF_F_ALL_TSO | NETIF_F_SG);
 		dev->features &= ~(NETIF_F_ALL_TSO | NETIF_F_SG);
-- 
2.20.1