On 02/08/13 07:04, George Neville-Neil wrote: > > On Feb 6, 2013, at 12:28 , Alfred Perlstein <bri...@mu.org> wrote: > >> On 2/6/13 4:46 AM, John Baldwin wrote: >>> On Wednesday, February 06, 2013 6:27:04 am Randall Stewart wrote: >>>> John: >>>> >>>> A burst at line rate will *often* cause drops. This is because >>>> router queues are at a finite size. Also such a burst (especially >>>> on a long delay bandwidth network) cause your RTT to increase even >>>> if there is no drop which is going to hurt you as well. >>>> >>>> A SHOULD in an RFC says you really really really really need to do it >>>> unless there is some thing that makes you willing to override it. It is >>>> slight wiggle room. >>>> >>>> In this I agree with Andre, we should not be *not* doing it. Otherwise >>>> folks will be turning this on and it is plain wrong. It may be fine >>>> for your network but I would not want to see it in FreeBSD. >>>> >>>> In my testing here at home I have put back into our stack max-burst. This >>>> uses Mark Allman's version (not Kacheong Poon's) where you clamp the cwnd >>>> at >>>> no more than 4 packets larger than your flight. All of my testing >>>> high-bw-delay or lan has shown this to improve TCP performance. This >>>> is because it helps you avoid bursting out so many packets that you >>>> overflow >>>> a queue. >>>> >>>> In your long-delay bw link if you do burst out too many (and you never >>>> know how many that is since you can not predict how full all those >>>> MPLS queues are or how big they are) you will really hurt yourself even >>>> worse. >>>> Note that generally in Cisco routers the default queue size is somewhere >>>> between >>>> 100-300 packets depending on the router. >>> Due to the way our application works this never happens, but I am fine with >>> just keeping this patch private. If there are other shops that need this >>> they >>> can always dig the patch up from the archives. >>> >> This is yet another time when I'm sad about how things happen in FreeBSD. >> >> A developer come forward with a non-default option that's very useful for >> some specific workloads, specifically one that contributes much time and $$$ >> to the project and the community rejects the patches even though it's been >> successful in other OSes. >> >> It makes zero sense. >> >> John, can you repost the patch? Maybe there is a way to refactor this >> somehow so it's like accept filters where we can plug in a hook for TCP? >> >> I am very disappointed, but not surprised. >> > > I take away the complete opposite feeling. This is how we work through these > issues. > It's clear from the discussion that this need not be a default in the system, > and is a special case. We had a reasoned discussion of what would be best to > do > and at least two experts in TCP weighed in on the effect this change might > have. > > Not everything proposed by a developer need go into the tree, in particular > since these > discussions are archived we can always revisit this later. > > This is exactly how collaborative development should look, whether or not the > patch > is integrated now, next week, next year, or ever.
+1 Whilst I would argue that some red herrings have been put forward in this thread, its progression is far from disappointing IMO. This is a sensitive area that requires careful scrutiny, independent of what our peers working on other OSes have decided is best for them. Cheers, Lawrence _______________________________________________ freebsd-net@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-net To unsubscribe, send any mail to "freebsd-net-unsubscr...@freebsd.org"
