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From: jigsaw <jigsaw@gmail.com>
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Subject: [dpdk-dev]  Need comment on 82599 TSO
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Hi,

I'm working on TSO for 82599, and encounter a problem: nowhere to store MSS.

TSO must be aware of MSS, or gso in skb of kernel.
But MSS nees 16 bits per mbuf. And we have no spare 16 bits in
rte_mbuf or rte_pktmbuf.
If we add 16 bit field in rte_pktmbuf, the size of rte_mbuf will be
doubled, coz currently the size is at the edge of cacheline(32 byte).

I have two solutions here:

1. Store MSS in struct rte_eth_conf.
This is actually a very bad idea, coz MSS is not bound to device.

2. Turn on and off TSO with rte_ctrlmbuf.
I found that rte_ctrlmbuf is not used at all. So it could be the first
use case of it.
With rte_ctrlmbuf we have enough space to store MSS.

Looking forward to your comments.

thx &
rgds,
-Qinglai