On 12/12/19 7:47 AM, Johannes Berg wrote: > Hi Neal, > > On Thu, 2019-12-12 at 10:11 -0500, Neal Cardwell wrote: >> On Thu, Dec 12, 2019 at 9:50 AM Johannes Berg <johannes@xxxxxxxxxxxxxxxx> wrote: >>> If you have any thoughts on this, I'd appreciate it. >> >> Thanks for the detailed report! > > Well, it wasn't. For example, I neglected to mention that I have to > actually use at least 2 TCP streams (but have tried up to 20) in order > to not run into the gbit link limit on the AP :-) > >> I was curious: >> >> o What's the sender's qdisc configuration? > > There's none, mac80211 bypasses qdiscs in favour of its internal TXQs > with FQ/codel. > >> o Would you be able to log periodic dumps (e.g. every 50ms or 100ms) >> of the test connection using a recent "ss" binary and "ss -tinm", to >> hopefully get a sense of buffer parameters, and whether the flow in >> these cases is being cwnd-limited, pacing-limited, >> send-buffer-limited, or receive-window-limited? > > Sure, though I'm not sure my ss is recent enough for what you had in > mind - if not I'll have to rebuild it (it was iproute2-ss190708). > > https://p.sipsolutions.net/3e515625bf13fa69.txt > > Note there are 4 connections (iperf is being used) but two are control > and two are data. Easy to see the difference really :-) > >> o Would you be able to share a headers-only tcpdump pcap trace? > > I'm not sure how to do headers-only, but I guess -s100 will work. > > https://johannes.sipsolutions.net/files/he-tcp.pcap.xz > Lack of GRO on receiver is probably what is killing performance, both for receiver (generating gazillions of acks) and sender (to process all these acks) I had a plan about enabling compressing ACK as I did for SACK in commit https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=5d9f4262b7ea41ca9981cc790e37cca6e37c789e But I have not done it yet. It is a pity because this would tremendously help wifi I am sure.
