linux-kernel - Small MSS in vmxnet3

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Date:   Sat, 23 Sep 2023 12:12:46 +1000
From:   Naruto Nguyen <narutonguyen2018@...il.com>
To:     kernel derkeiler <linux-kernel@...r.kernel.org>,
        kernelnewbies <kernelnewbies@...nelnewbies.org>
Subject: Small MSS in vmxnet3

Hello everyone,

Recently I found that packets sent from vmxnet3 driver on guest have
MSS value set to very small size, some 10 bytes, some 25 bytes MSS.
The vmxnet3 NIC enables TSO. Could you let me know any possible reason
that the packets are fragmented with very small MSS.and is it normal?.
Any way to avoid this small MSS or it's just normal.

In addition, when enabling debug for vmxnet3, in function
vmxnet3_tq_xmit, it has a printout

netdev_dbg(adapter->netdev,
"txd[%u]: SOP 0x%Lx 0x%x 0x%x\n",
(u32)(ctx.sop_txd -
tq->tx_ring.base), le64_to_cpu(gdesc->txd.addr),
le32_to_cpu(gdesc->dword[2]), le32_to_cpu(gdesc->dword[3]));

could you suggest an easier way to extract the MSS value from this output?

Thanks,
Kind regards, Naruto