hw/net/rtl8139.c | 13 ++++++++----- 1 file changed, 8 insertions(+), 5 deletions(-)
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 <stefanha@redhat.com>
Sent: Tuesday, 15 November 2022 17:37
To: qemu-devel@nongnu.org
Cc: jasowang@redhat.com; qemu-stable@nongnu.org; Stefan Hajnoczi <stefanha@redhat.com>; Russell King - ARM Linux <linux@armlinux.org.uk>; Tobias Fiebig <tobias+git@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 <linux@armlinux.org.uk>
Reported-by: Tobias Fiebig <tobias+git@fiebig.nl>
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1312
Signed-off-by: Stefan Hajnoczi <stefanha@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,
--
2.38.1On Wed, Nov 16, 2022 at 7:43 AM Tobias Fiebig <tobias@fiebig.nl> wrote:
>
> 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
It might be also helpful to dump mss saw by Qemu to see if it really
changes or differs a lot from 1500.
Thanks
>
> -----Original Message-----
> From: Stefan Hajnoczi <stefanha@redhat.com>
> Sent: Tuesday, 15 November 2022 17:37
> To: qemu-devel@nongnu.org
> Cc: jasowang@redhat.com; qemu-stable@nongnu.org; Stefan Hajnoczi <stefanha@redhat.com>; Russell King - ARM Linux <linux@armlinux.org.uk>; Tobias Fiebig <tobias+git@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 <linux@armlinux.org.uk>
> Reported-by: Tobias Fiebig <tobias+git@fiebig.nl>
> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1312
> Signed-off-by: Stefan Hajnoczi <stefanha@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
>
>
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