Hi Stephen, Thanks for comment. Pls check the other thread that I just posted.
thx & rgds, -Qinglai On Fri, Oct 4, 2013 at 7:41 PM, Stephen Hemminger <stephen at networkplumber.org> wrote: > On Fri, 4 Oct 2013 15:44:19 +0300 > jigsaw <jigsaw at gmail.com> wrote: > >> 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 > > The mbuf needs to grow to 2 cache lines. There are other things that need > to be added to mbuf eventually as well. For example the QoS bitfield is > too small when crammed into 32 bits. Ideally the normal small packet > stuff would be in the first cacheline; and the other part of the struct > would have things less likely to be used.
