Heho, Just to keep you in the loop; Just applied the patch, but things didn't really get better; I am currently doing a 'make clean; make' for good measure (had built head first), and will also double-check that there is no accidental use of system-qemu libs.
If that still doesn't show an effect, I'll hold tcpdump to the wire again. With best regards, Tobias -----Original Message----- From: Stefan Hajnoczi <stefa...@redhat.com> Sent: Tuesday, 15 November 2022 17:37 To: qemu-devel@nongnu.org Cc: jasow...@redhat.com; qemu-sta...@nongnu.org; Stefan Hajnoczi <stefa...@redhat.com>; Russell King - ARM Linux <li...@armlinux.org.uk>; Tobias Fiebig <tobias+...@fiebig.nl> Subject: [PATCH for-7.2] rtl8139: honor large send MSS value 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 <li...@armlinux.org.uk> Reported-by: Tobias Fiebig <tobias+...@fiebig.nl> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1312 Signed-off-by: Stefan Hajnoczi <stefa...@redhat.com> --- 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 ) ) #define ETHER_TYPE_LEN 2 -#define ETH_MTU 1500 #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) int large_send_mss = (txdw0 >> 16) & 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; @@ -2177,9 +2176,13 @@ static int rtl8139_cplus_transmit_one(RTL8139State *s) goto skip_offload; } - /* ETH_MTU = ip header len + tcp header len + payload */ + /* MSS too small? */ + if (tcp_hlen + hlen >= large_send_mss) { + goto skip_offload; + } + int tcp_data_len = ip_data_len - tcp_hlen; - int tcp_chunk_size = ETH_MTU - hlen - tcp_hlen; + int tcp_chunk_size = large_send_mss - 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, -- 2.38.1
