From 6d71357a3b651ec9db126e4862b77e13165427f5 Mon Sep 17 00:00:00 2001 From: Stefan Hajnoczi Date: Thu, 17 Nov 2022 11:55:54 -0500 Subject: [PATCH] rtl8139: honor large send MSS value MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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. Jason Wang noticed that the Large-Send MSS value mask was incorrect so it is adjusted to match the datasheet and Linux 8139cp driver. 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 Acked-by: Jason Wang Reviewed-by: Philippe Mathieu-Daudé Signed-off-by: Stefan Hajnoczi Message-Id: <20221117165554.1773409-4-stefanha@redhat.com> --- hw/net/rtl8139.c | 26 ++++++++++++-------------- 1 file changed, 12 insertions(+), 14 deletions(-) diff --git a/hw/net/rtl8139.c b/hw/net/rtl8139.c index 6dd7a8e6e0..700b1b66b6 100644 --- a/hw/net/rtl8139.c +++ b/hw/net/rtl8139.c @@ -77,7 +77,6 @@ ( ( input ) & ( size - 1 ) ) #define ETHER_TYPE_LEN 2 -#define ETH_MTU 1500 #define VLAN_TCI_LEN 2 #define VLAN_HLEN (ETHER_TYPE_LEN + VLAN_TCI_LEN) @@ -1934,8 +1933,9 @@ static int rtl8139_cplus_transmit_one(RTL8139State *s) #define CP_TX_LS (1<<28) /* large send packet flag */ #define CP_TX_LGSEN (1<<27) -/* large send MSS mask, bits 16...25 */ -#define CP_TC_LGSEN_MSS_MASK ((1 << 12) - 1) +/* large send MSS mask, bits 16...26 */ +#define CP_TC_LGSEN_MSS_SHIFT 16 +#define CP_TC_LGSEN_MSS_MASK ((1 << 11) - 1) /* IP checksum offload flag */ #define CP_TX_IPCS (1<<18) @@ -2152,10 +2152,11 @@ static int rtl8139_cplus_transmit_one(RTL8139State *s) goto skip_offload; } - int large_send_mss = (txdw0 >> 16) & CP_TC_LGSEN_MSS_MASK; + int large_send_mss = (txdw0 >> CP_TC_LGSEN_MSS_SHIFT) & + CP_TC_LGSEN_MSS_MASK; - DPRINTF("+++ C+ mode offloaded task TSO MTU=%d IP data %d " - "frame data %d specified MSS=%d\n", ETH_MTU, + DPRINTF("+++ C+ mode offloaded task TSO IP data %d " + "frame data %d specified MSS=%d\n", ip_data_len, saved_size - ETH_HLEN, large_send_mss); int tcp_send_offset = 0; @@ -2180,25 +2181,22 @@ static int rtl8139_cplus_transmit_one(RTL8139State *s) goto skip_offload; } - /* ETH_MTU = ip header len + tcp header len + payload */ int tcp_data_len = ip_data_len - tcp_hlen; - int tcp_chunk_size = ETH_MTU - hlen - tcp_hlen; DPRINTF("+++ C+ mode TSO IP data len %d TCP hlen %d TCP " - "data len %d TCP chunk size %d\n", ip_data_len, - tcp_hlen, tcp_data_len, tcp_chunk_size); + "data len %d\n", ip_data_len, tcp_hlen, tcp_data_len); /* note the cycle below overwrites IP header data, but restores it from saved_ip_header before sending packet */ int is_last_frame = 0; - for (tcp_send_offset = 0; tcp_send_offset < tcp_data_len; tcp_send_offset += tcp_chunk_size) + for (tcp_send_offset = 0; tcp_send_offset < tcp_data_len; tcp_send_offset += large_send_mss) { - uint16_t chunk_size = tcp_chunk_size; + uint16_t chunk_size = large_send_mss; /* check if this is the last frame */ - if (tcp_send_offset + tcp_chunk_size >= tcp_data_len) + if (tcp_send_offset + large_send_mss >= tcp_data_len) { is_last_frame = 1; chunk_size = tcp_data_len - tcp_send_offset; @@ -2247,7 +2245,7 @@ static int rtl8139_cplus_transmit_one(RTL8139State *s) ip->ip_len = cpu_to_be16(hlen + tcp_hlen + chunk_size); /* increment IP id for subsequent frames */ - ip->ip_id = cpu_to_be16(tcp_send_offset/tcp_chunk_size + be16_to_cpu(ip->ip_id)); + ip->ip_id = cpu_to_be16(tcp_send_offset/large_send_mss + be16_to_cpu(ip->ip_id)); ip->ip_sum = 0; ip->ip_sum = ip_checksum(eth_payload_data, hlen);