We enable TSO to get a lot of data at once to build A-MSDUs. Our hardware doesn't have (yet) TCP CSUM offload, so we do it manually. TSO won't be enabled on hardware that don't support CSUM offload in release code, computing TCP CSUM in the driver is just a way to start coding the flows. This is why the "CSUM offload" implementation in the driver in so bad in terms of efficiency. I preferred to have the flows as close as they will be when the hardware will be able to the CSUM than to try to seek efficiency. The hardware that will have CSUM offload will still require the driver to split the skb in software including the IP / TCP header copy and update etc... We could have enabled A-MSDU based on xmit-more, but the rationale of using LSO is that when using pfifo-fast, the Qdisc gets one packet and dequeues is straight away which limits the possibility to get a lot of packets at once. (Am I right here?). A note about A-MSDUs for non-wireless people: ********************************************* An A-MSDU is a aggregated frame. It is one big 802.11 packet that contains several subframes. Each subframe is a TCP segment. One A-MSDU is represented by one single skb which means that we need to copy / duplicate the TCP / IP / SNAP headers in one single skb. This is why those headers are copied to a separate page: that page is added multiple times to the skb with different offsets. Each subframes needs at least 2 frags: 1 for the headers, 1 (or more) for the payload. I am quite a newbie in skb handling, so I guess that this code can be improved. I have tested it decently using iperf, but this doesn't mean that there are no issues using other applications. We are enabling pktgen on TCP (using patches that were sent a year ago or so) to test the different layouts of the skb (payload partition amongst the header and the different frags). I'll be very happy to get comments on that code, this is why I am sending it to netdev as well since the TSO experts are there :) Emmanuel Grumbach (3): iwlwifi: mvm: add real TSO implementation iwlwifi: mvm: allow to create A-MSDUs from a large send iwlwifi: mvm: transfer the truesize to the last TSO segment drivers/net/wireless/iwlwifi/mvm/mac80211.c | 3 +- drivers/net/wireless/iwlwifi/mvm/sta.c | 4 +- drivers/net/wireless/iwlwifi/mvm/sta.h | 6 +- drivers/net/wireless/iwlwifi/mvm/tx.c | 669 ++++++++++++++++++++++++++-- 4 files changed, 647 insertions(+), 35 deletions(-) -- 2.1.4 -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
