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bh=0V9FW4XgRhJvhlV4mqFDlfCynvDX4A/FbUDSpDmXChc=; b=AFRyQA/QHxmkEADSpdbbzgMTLrcQlm7JSnoG7xOCP/GwGFtUBCr2C0xbPwLCFudivkNFU6 6jVTF4QM2sH3BeBmHApdtZzqu3ZkVBRGwgf7LWOLyLz4chS8ZOL2jvPZWWM6JnpxZD8ZAQ zrQVOXiksoNsD3+W4HgifzAx5FOa0ow= X-MC-Unique: goINLCQPNi2SEylKk-NQRg-1 From: Stefan Hajnoczi To: qemu-devel@nongnu.org Cc: jasowang@redhat.com, qemu-stable@nongnu.org, Stefan Hajnoczi , Russell King - ARM Linux , Tobias Fiebig Subject: [PATCH for-7.2] rtl8139: honor large send MSS value Date: Tue, 15 Nov 2022 11:36:59 -0500 Message-Id: <20221115163659.1595865-1-stefanha@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.1 on 10.11.54.1 Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=170.10.129.124; envelope-from=stefanha@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: qemu-devel-bounces+importer=patchew.org@nongnu.org X-ZohoMail-DKIM: pass (identity @redhat.com) X-ZM-MESSAGEID: 1668530305626100003 Content-Type: text/plain; charset="utf-8" The Large-Send Task Offload Tx Descriptor (9.2.1 Transmit) has a Large-Send MSS value where the driver specifies the MSS. See the datasheet here: http://realtek.info/pdf/rtl8139cp.pdf The code ignores this value and uses a hardcoded MSS of 1500 bytes instead. When the MTU is less than 1500 bytes the hardcoded value results in IP fragmentation and poor performance. Use the Large-Send MSS value to correctly size Large-Send packets. This issue was discussed in the past here: https://lore.kernel.org/all/20161114162505.GD26664@stefanha-x1.localdomain/ Reported-by: Russell King - ARM Linux Reported-by: Tobias Fiebig Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1312 Signed-off-by: Stefan Hajnoczi Acked-by: Jason Wang --- hw/net/rtl8139.c | 13 ++++++++----- 1 file changed, 8 insertions(+), 5 deletions(-) Tobias: Please test this fix. Thanks! diff --git a/hw/net/rtl8139.c b/hw/net/rtl8139.c index e6643e3c9d..ecc4dcb07f 100644 --- a/hw/net/rtl8139.c +++ b/hw/net/rtl8139.c @@ -77,7 +77,6 @@ ( ( input ) & ( size - 1 ) ) =20 #define ETHER_TYPE_LEN 2 -#define ETH_MTU 1500 =20 #define VLAN_TCI_LEN 2 #define VLAN_HLEN (ETHER_TYPE_LEN + VLAN_TCI_LEN) @@ -2151,8 +2150,8 @@ static int rtl8139_cplus_transmit_one(RTL8139State *s) =20 int large_send_mss =3D (txdw0 >> 16) & CP_TC_LGSEN_MSS_MAS= K; =20 - DPRINTF("+++ C+ mode offloaded task TSO MTU=3D%d IP data %= d " - "frame data %d specified MSS=3D%d\n", ETH_MTU, + DPRINTF("+++ C+ mode offloaded task TSO IP data %d " + "frame data %d specified MSS=3D%d\n", ip_data_len, saved_size - ETH_HLEN, large_send_mss); =20 int tcp_send_offset =3D 0; @@ -2177,9 +2176,13 @@ static int rtl8139_cplus_transmit_one(RTL8139State *= s) goto skip_offload; } =20 - /* ETH_MTU =3D ip header len + tcp header len + payload */ + /* MSS too small? */ + if (tcp_hlen + hlen >=3D large_send_mss) { + goto skip_offload; + } + int tcp_data_len =3D ip_data_len - tcp_hlen; - int tcp_chunk_size =3D ETH_MTU - hlen - tcp_hlen; + int tcp_chunk_size =3D large_send_mss - hlen - tcp_hlen; =20 DPRINTF("+++ C+ mode TSO IP data len %d TCP hlen %d TCP " "data len %d TCP chunk size %d\n", ip_data_len, --=20 2.38.1