net/gve: Update max_rx_pktlen to be based on MTU
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Commit Message
Before this patch, max_rx_pktlen was always set to UINT16_MAX. This, in
conjunction with the MTU fix, causes problems with testpmd, as setting the
packet length with the --max-pkt-len flag causes the MTU to be set
higher than possible due to underflow.
As an example, setting --max-pkt-len=1460 (the default MTU on Google
Cloud VMs) causes testpmd to set the following:
mtu = 1460 - eth_overhead,
where eth_overhead = dev->max_rx_pktlen - dev->max_mtu = 65535 - 1460.
Thus, mtu = 1460 - 65535 + 1460 = 2921 due to underflow.
Signed-off-by: Joshua Washington <joshwash@google.com>
Fixes: 030025b74202 ("net/gve: fix max MTU limit")
Cc: joshwash@google.com
---
drivers/net/gve/gve_ethdev.c | 2 +-
drivers/net/gve/gve_ethdev.h | 1 -
2 files changed, 1 insertion(+), 2 deletions(-)
Comments
On Mon, 16 Oct 2023 13:59:48 -0700
Joshua Washington <joshwash@google.com> wrote:
> Before this patch, max_rx_pktlen was always set to UINT16_MAX. This, in
> conjunction with the MTU fix, causes problems with testpmd, as setting the
> packet length with the --max-pkt-len flag causes the MTU to be set
> higher than possible due to underflow.
>
> As an example, setting --max-pkt-len=1460 (the default MTU on Google
> Cloud VMs) causes testpmd to set the following:
> mtu = 1460 - eth_overhead,
>
> where eth_overhead = dev->max_rx_pktlen - dev->max_mtu = 65535 - 1460.
>
> Thus, mtu = 1460 - 65535 + 1460 = 2921 due to underflow.
>
> Signed-off-by: Joshua Washington <joshwash@google.com>
This seems wrong and is not what other drivers do.
Other drivers give the absolute maximum in the dev_info so that
application can size accordingly.
On Mon, 16 Oct 2023 13:59:48 -0700
Joshua Washington <joshwash@google.com> wrote:
> conjunction with the MTU fix, causes problems with testpmd, as setting the
> packet length with the --max-pkt-len flag causes the MTU to be set
> higher than possible due to underflow.
>
> As an example, setting --max-pkt-len=1460 (the default MTU on Google
> Cloud VMs) causes testpmd to set the following:
> mtu = 1460 - eth_overhead,
>
> where eth_overhead = dev->max_rx_pktlen - dev->max_mtu = 65535 - 1460.
>
> Thus, mtu = 1460 - 65535 + 1460 = 2921 due to underflow.
>
> Signed-off-by: Joshua Washington <joshwash@google.com>
>
> Fixes: 030025b74202 ("net/gve: fix max MTU limit")
> Cc: joshwash@google.com
Never mind, previous comment.
You are correctly doing the inverse of this common code pattern.
In testpmd:
static uint32_t
eth_dev_get_overhead_len(uint32_t max_rx_pktlen, uint16_t max_mtu)
{
uint32_t overhead_len;
if (max_mtu != UINT16_MAX && max_rx_pktlen > max_mtu)
overhead_len = max_rx_pktlen - max_mtu;
else
overhead_len = RTE_ETHER_HDR_LEN + RTE_ETHER_CRC_LEN;
return overhead_len;
}
On 10/16/2023 9:59 PM, Joshua Washington wrote:
> Before this patch, max_rx_pktlen was always set to UINT16_MAX. This, in
> conjunction with the MTU fix, causes problems with testpmd, as setting the
> packet length with the --max-pkt-len flag causes the MTU to be set
> higher than possible due to underflow.
>
> As an example, setting --max-pkt-len=1460 (the default MTU on Google
> Cloud VMs) causes testpmd to set the following:
> mtu = 1460 - eth_overhead,
>
> where eth_overhead = dev->max_rx_pktlen - dev->max_mtu = 65535 - 1460.
>
> Thus, mtu = 1460 - 65535 + 1460 = 2921 due to underflow.
>
> Signed-off-by: Joshua Washington <joshwash@google.com>
>
> Fixes: 030025b74202 ("net/gve: fix max MTU limit")
> Cc: joshwash@google.com
>
Cc: stable@dpdk.org
Applied to dpdk-next-net/main, thanks.
@@ -297,7 +297,7 @@ gve_dev_info_get(struct rte_eth_dev *dev, struct rte_eth_dev_info *dev_info)
dev_info->max_rx_queues = priv->max_nb_rxq;
dev_info->max_tx_queues = priv->max_nb_txq;
dev_info->min_rx_bufsize = GVE_MIN_BUF_SIZE;
- dev_info->max_rx_pktlen = GVE_MAX_RX_PKTLEN;
+ dev_info->max_rx_pktlen = priv->max_mtu + RTE_ETHER_HDR_LEN;
dev_info->max_mtu = priv->max_mtu;
dev_info->min_mtu = RTE_ETHER_MIN_MTU;
@@ -21,7 +21,6 @@
#define GVE_TX_MAX_FREE_SZ 512
#define GVE_MIN_BUF_SIZE 1024
-#define GVE_MAX_RX_PKTLEN 65535
#define GVE_TX_CKSUM_OFFLOAD_MASK ( \
RTE_MBUF_F_TX_L4_MASK | \