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rtl8139: honor large send MSS value

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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 <jasowang@redhat.com> 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 <linux@armlinux.org.uk>
Reported-by: Tobias Fiebig <tobias+git@fiebig.nl>
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1312
Acked-by: Jason Wang <jasowang@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-Id: <20221117165554.1773409-4-stefanha@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2022-11-17 11:55:54 -05:00
parent c74831a02c
commit 6d71357a3b
1 changed files with 12 additions and 14 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

26
hw/net/rtl8139.c
View File

@ -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);