On 12/28/2020 2:51 PM, Andrew Rybchenko wrote:

On 12/17/20 12:22 PM, Steve Yang wrote:

quoted

If max rx packet length is smaller then MTU + Ether overhead, that will
drop all MTU size packets.

Update the MTU size according to the max rx packet and Ether overhead.

Fixes: 59d0ecdbf0e1 ("ethdev: MTU accessors")

Signed-off-by: Steve Yang <redacted>
---
  lib/librte_ethdev/rte_ethdev.c | 21 ++++++++++++++++++---
  1 file changed, 18 insertions(+), 3 deletions(-)

diff --git a/lib/librte_ethdev/rte_ethdev.c b/lib/librte_ethdev/rte_ethdev.c
index 17ddacc78d..ff6a1e675f 100644
--- a/lib/librte_ethdev/rte_ethdev.c
+++ b/lib/librte_ethdev/rte_ethdev.c

@@ -1292,6 +1292,7 @@ rte_eth_dev_configure(uint16_t port_id, uint16_t nb_rx_q, uint16_t nb_tx_q,
  	struct rte_eth_dev *dev;
  	struct rte_eth_dev_info dev_info;
  	struct rte_eth_conf orig_conf;
+	uint16_t overhead_len;
  	int diag;
  	int ret;
  

@@ -1323,6 +1324,15 @@ rte_eth_dev_configure(uint16_t port_id, uint16_t nb_rx_q, uint16_t nb_tx_q,
  	if (ret != 0)
  		goto rollback;
  
+	/* Get the real Ethernet overhead length */
+	if (dev_info.max_mtu &&

First of all I'm not sure that we need to handle 0 value
separately. Or it should be checked separately and trigger
an error since it is a driver mis-behaviour.

Agree. Most probably we can drop it, "dev_info.max_mtu != UINT16_MAX" covers the 
case driver doesn't provide any value.

If kept, it should be compared vs 0 explicitly in accordance
with DPDK coding style.

quoted

+	    dev_info.max_mtu != UINT16_MAX &&
+	    dev_info.max_rx_pktlen &&

It should be compared vs 0 explicitly in accordance
with DPDK coding style.

quoted

+	    dev_info.max_rx_pktlen > dev_info.max_mtu)
+		overhead_len = dev_info.max_rx_pktlen - dev_info.max_mtu;
+	else
+		overhead_len = RTE_ETHER_HDR_LEN + RTE_ETHER_CRC_LEN;
+
  	/* If number of queues specified by application for both Rx and Tx is
  	 * zero, use driver preferred values. This cannot be done individually
  	 * as it is valid for either Tx or Rx (but not both) to be zero.

@@ -1410,13 +1420,18 @@ rte_eth_dev_configure(uint16_t port_id, uint16_t nb_rx_q, uint16_t nb_tx_q,
  			goto rollback;
  		}
  	} else {
-		if (dev_conf->rxmode.max_rx_pkt_len < RTE_ETHER_MIN_LEN ||
-			dev_conf->rxmode.max_rx_pkt_len > RTE_ETHER_MAX_LEN)
+		uint16_t pktlen = dev_conf->rxmode.max_rx_pkt_len;
+		if (pktlen < RTE_ETHER_MIN_MTU + overhead_len ||
+			pktlen > RTE_ETHER_MTU + overhead_len)

Alignment looks misleading. Either two tabs or just 4 spaces.

quoted

  			/* Use default value */
  			dev->data->dev_conf.rxmode.max_rx_pkt_len =
-							RTE_ETHER_MAX_LEN;
+						RTE_ETHER_MTU + overhead_len;
  	}
  
+	/* Scale the MTU size to adapt max_rx_pkt_len */
+	dev->data->mtu = dev->data->dev_conf.rxmode.max_rx_pkt_len -
+				overhead_len;
+

Is it expected side effect that re-configure always resets
previously set MTU. I.e.:
    configure -> set_mtu -> start -> stop -> re-configure
and set MTU is lost.

This is the problem of two APIs updating same/related values, when device 
re-configure with a given 'max_rx_pkt_len', can we know if the intentions is 
update to the value to new provided 'max_rx_pkt_len' or not?

For this case if user want to keep the MTU value, can read the MTU from device 
first and set 'max_rx_pkt_len' according it.

And we can reduce to updating the MTU in the configure() only when JUMBO frame 
offload is requested, that should be when the 'max_rx_pkt_len' is valid only.

quoted

  	/*
  	 * If LRO is enabled, check that the maximum aggregated packet
  	 * size is supported by the configured device.