[RFC v2 0/3] add TSO / A-MSDU TX for iwlwifi
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 majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [RFC v2 0/3] add TSO / A-MSDU TX for iwlwifi
On Wed, 2015-08-19 at 15:59 +0300, Emmanuel Grumbach wrote: 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?). No, you are not ;) Key point for xmit_more is BQL being implemented in your driver. Relevant code is in try_bulk_dequeue_skb() -- To unsubscribe from this list: send the line unsubscribe linux-wireless in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [RFC v2 0/3] add TSO / A-MSDU TX for iwlwifi
On Wed, 2015-08-19 at 17:00 +, Grumbach, Emmanuel wrote: On 08/19/2015 07:08 PM, Eric Dumazet wrote: On Wed, 2015-08-19 at 15:07 +, Grumbach, Emmanuel wrote: I'll look at it. I was almost starting to implement that but then I thought with another (good?) reason to use LSO. LSO gives me the guarantee that the packet is directed to one peer, which might not be the case with xmit_more since we have one Qdisc for several clients in case we are in AP mode. Building an A-MSDU for several clients is not possible, at least not for several client in the L2 (different MAC addresses). LSO avoids this problem completely. Then, simply calling skb_gso_segment() from the driver might be enough, and less work for you. This would even support TSO on IPv6 Well... I did take care of IPv6. net/core/tso.c does not yet handle IPv6 -- To unsubscribe from this list: send the line unsubscribe linux-wireless in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [RFC v2 0/3] add TSO / A-MSDU TX for iwlwifi
On 08/19/2015 07:08 PM, Eric Dumazet wrote: On Wed, 2015-08-19 at 15:07 +, Grumbach, Emmanuel wrote: I'll look at it. I was almost starting to implement that but then I thought with another (good?) reason to use LSO. LSO gives me the guarantee that the packet is directed to one peer, which might not be the case with xmit_more since we have one Qdisc for several clients in case we are in AP mode. Building an A-MSDU for several clients is not possible, at least not for several client in the L2 (different MAC addresses). LSO avoids this problem completely. Then, simply calling skb_gso_segment() from the driver might be enough, and less work for you. This would even support TSO on IPv6 Well... I did take care of IPv6. segs = skb_gso_segment(skb, tp-dev-features ~(NETIF_F_TSO | NETIF_F_TSO6)); Thing is that our HW layers are currently implemented to receive one skb per 802.11 packet. So that if I call skb_gso_segment, I'd have to re-assemble the segs into one A-MSDU which would translate one skb. I guess I could change the HW layer in the driver to be able to get a list of skbs and make a single packet out of it, but that'd be tricky or wasteful. skb_gso_segment will duplicate the wifi header while it is not needed. Only the TCP / IP / SNAP headers need to be duplicated. Moreover, each subframe in the A-MSDU needs it own subframe header (same format as ethhdr) and there is also some padding in there. So that would be even more complicated IMHO. My code doesn't copy any payload. Only the headers. This is why I thought it'd be better than segmenting and then re-assembling. I did call skb_gso_segment if I get lots of payload in the header (more than 2 * mss) in order to simplify the implementation. -- To unsubscribe from this list: send the line unsubscribe linux-wireless in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [RFC v2 0/3] add TSO / A-MSDU TX for iwlwifi
On Wed, 2015-08-19 at 17:56 +, Grumbach, Emmanuel wrote: So I feel that making net/core/tso.c more complicated just because of our craziness seems an overkill to me. I'll try a bit harder to see how I can use net/core/tso.c, but I have to say I am pessimistic. net/core/tso.c is WIP, feel free to expand it to make it more generic and meet your needs. The point is : we want a core infrastructure, not something that each individual driver implements in ~500 lines of code :( -- To unsubscribe from this list: send the line unsubscribe linux-wireless in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
