Coexist how? Do you mean that one socket can use one and a different socket uses the other? That makes sense.
On Thu, Jul 18, 2024 at 10:34 AM <tue...@freebsd.org> wrote: > > > On 18. Jul 2024, at 15:00, Junho Choi <junho.c...@gmail.com> wrote: > > > > Alan - this is a great result to see. Thanks for experimenting. > > > > Just curious why bbr and rack don't co-exist? Those are two separate things. > > Is it a current bug or by design? > Technically RACK and BBR can coexist. The problem was with pf and/or LRO. > > But this is all fixed now in 14.1 and head. > > Best regards > Michael > > > > BR, > > > > On Thu, Jul 18, 2024 at 5:27 AM <tue...@freebsd.org> wrote: > >> On 17. Jul 2024, at 22:00, Alan Somers <asom...@freebsd.org> wrote: > >> > >> On Sat, Jul 13, 2024 at 1:50 AM <tue...@freebsd.org> wrote: > >>> > >>>> On 13. Jul 2024, at 01:43, Alan Somers <asom...@freebsd.org> wrote: > >>>> > >>>> I've been experimenting with RACK and BBR. In my environment, they > >>>> can dramatically improve single-stream TCP performance, which is > >>>> awesome. But pf interferes. I have to disable pf in order for them > >>>> to work at all. > >>>> > >>>> Is this a known limitation? If not, I will experiment some more to > >>>> determine exactly what aspect of my pf configuration is responsible. > >>>> If so, can anybody suggest what changes would have to happen to make > >>>> the two compatible? > >>> A problem with same symptoms was already reported and fixed in > >>> https://reviews.freebsd.org/D43769 > >>> > >>> Which version are you using? > >>> > >>> Best regards > >>> Michael > >>>> > >>>> -Alan > >> > >> TLDR; tcp_rack is good, cc_chd is better, and tcp_bbr is best > >> > >> I want to follow up with the list to post my conclusions. Firstly > >> tuexen@ helped me solve my problem: in FreeBSD 14.0 there is a 3-way > >> incompatibility between (tcp_bbr || tcp_rack) && lro && pf. I can > >> confirm that tcp_bbr works for me if I either disable LRO, disable PF, > >> or switch to a 14.1 server. > >> > >> Here's the real problem: on multiple production servers, downloading > >> large files (or ZFS send/recv streams) was slow. After ruling out > >> many possible causes, wireshark revealed that the connection was > >> suffering about 0.05% packet loss. I don't know the source of that > >> packet loss, but I don't believe it to be congestion-related. Along > >> with a 54ms RTT, that's a fatal combination for the throughput of > >> loss-based congestion control algorithms. According to the Mathis > >> Formula [1], I could only expect 1.1 MBps over such a connection. > >> That's actually worse than what I saw. With default settings > >> (cc_cubic), I averaged 5.6 MBps. Probably Mathis's assumptions are > >> outdated, but that's still pretty close for such a simple formula > >> that's 27 years old. > >> > >> So I benchmarked all available congestion control algorithms for > >> single download streams. The results are summarized in the table > >> below. > >> > >> Algo Packet Loss Rate Average Throughput > >> vegas 0.05% 2.0 MBps > >> newreno 0.05% 3.2 MBps > >> cubic 0.05% 5.6 MBps > >> hd 0.05% 8.6 MBps > >> cdg 0.05% 13.5 MBps > >> rack 0.04% 14 MBps > >> htcp 0.05% 15 MBps > >> dctcp 0.05% 15 MBps > >> chd 0.05% 17.3 MBps > >> bbr 0.05% 29.2 MBps > >> cubic 10% 159 kBps > >> chd 10% 208 kBps > >> bbr 10% 5.7 MBps > >> > >> RACK seemed to achieve about the same maximum bandwidth as BBR, though > >> it took a lot longer to get there. Also, with RACK, wireshark > >> reported about 10x as many retransmissions as dropped packets, which > >> is suspicious. > >> > >> At one point, something went haywire and packet loss briefly spiked to > >> the neighborhood of 10%. I took advantage of the chaos to repeat my > >> measurements. As the table shows, all algorithms sucked under those > >> conditions, but BBR sucked impressively less than the others. > >> > >> Disclaimer: there was significant run-to-run variation; the presented > >> results are averages. And I did not attempt to measure packet loss > >> exactly for most runs; 0.05% is merely an average of a few selected > >> runs. These measurements were taken on a production server running a > >> real workload, which introduces noise. Soon I hope to have the > >> opportunity to repeat the experiment on an idle server in the same > >> environment. > >> > >> In conclusion, while we'd like to use BBR, we really can't until we > >> upgrade to 14.1, which hopefully will be soon. So in the meantime > >> we've switched all relevant servers from cubic to chd, and we'll > >> reevaluate BBR after the upgrade. > > Hi Alan, > > > > just to be clear: the version of BBR currently implemented is > > BBR version 1, which is known to be unfair in certain scenarios. > > Google is still working on BBR to address this problem and improve > > it in other aspects. But there is no RFC yet and the updates haven't > > been implemented yet in FreeBSD. > > > > Best regards > > Michael > >> > >> [1]: https://www.slac.stanford.edu/comp/net/wan-mon/thru-vs-loss.html > >> > >> -Alan > > > > > > > > > > -- > > Junho Choi <junho dot choi at gmail.com> | https://saturnsoft.net >
