On Wed, Aug 14, 2013 at 8:46 PM, Lawrence Stewart <lstew...@freebsd.org> wrote: > On 08/15/13 02:44, Andre Oppermann wrote: >> On 14.08.2013 04:36, Lawrence Stewart wrote: >>> Hi Andre, >>> >>> [RE team is BCCed so they're aware of this discussion] >>> >>> On 07/06/13 00:58, Andre Oppermann wrote: >>>> Author: andre >>>> Date: Fri Jul 5 14:58:24 2013 >>>> New Revision: 252789 >>>> URL: http://svnweb.freebsd.org/changeset/base/252789 >>>> >>>> Log: >>>> MFC r242266: >>>> >>>> Increase the initial CWND to 10 segments as defined in IETF TCPM >>>> draft-ietf-tcpm-initcwnd-05. It explains why the increased initial >>>> window improves the overall performance of many web services without >>>> risking congestion collapse. >>>> >>>> As long as it remains a draft it is placed under a sysctl marking it >>>> as experimental: >>>> net.inet.tcp.experimental.initcwnd10 = 1 >>>> When it becomes an official RFC soon the sysctl will be changed to >>>> the RFC number and moved to net.inet.tcp. >>>> >>>> This implementation differs from the RFC draft in that it is a bit >>>> more conservative in the case of packet loss on SYN or SYN|ACK >>>> because >>>> we haven't reduced the default RTO to 1 second yet. Also the >>>> restart >>>> window isn't yet increased as allowed. Both will be adjusted with >>>> upcoming changes. >>>> >>>> Is is enabled by default. In Linux it is enabled since kernel 3.0. >>> >>> I haven't been fully alert to FreeBSD happenings this year so apologies >>> for bringing this up so long after the MFC. >>> >>> I don't think this change should have been MFCed, at least not in its >>> current form. Enabling the switch to IW=10 on a stable branch is >>> inappropriate IMO. I also think the "net.inet.tcp.experimental" sysctl >>> branch is poorly named as per the important discussion we had back in >>> February [1]. I would really prefer we didn't get stuck having to keep >>> it around by making a stable release with it being present. >>> >>> I think this commit should be backed out of stable/9 and more >>> importantly, 9.2-RELEASE. >> >> Backing out the patch isn't really necessary, just flip the switch to >> off having it revert to the RFC5681 defaults. Those who want it anyway >> can simply enable it again. > > That doesn't address the sysctl tree naming concern or mechanism issue - > please refer back to the Feb discussion; specifically the proposal to > rename the experimental branch to "net.inet.tcp.nonstandard" and add an > "allowed" leaf which takes a list of non-standard behaviours to allow > tweaking in the stack. > > Leaving the sysctl branch named "experimental" conveys that the things > which live under the branch are being evaluated in some way for becoming > a default, which is very different to "nonstandard" which conveys that > the user is twiddling things in a way which normally shouldn't be. IW=10 > may become a FreeBSD default at some point, but the mechanism for > enabling it should be to specify the initial window as a value in > segments, and as such by allowing any non-standard value (IW=7, IW=50), > I strongly argue in favour for changing the branch name from > "experimental" to "nonstandard". > > In order to continue this discussion in the context of what we started > in Feb, I still request that this change be backed out of releng/9.2 so > that 9.2-RELEASE doesn't ship with it. We can continue discussion for > it's future in stable/9 and head after the backout so that 9.2 isn't > held up. > >> IW10 has become RFC6928 (experimental) in April 2013. > > Great for the draft authors, but irrelevant for this discussion. > >>> As an aside, I am intending to follow up to the Feb discussion with a >>> patch that implements the basic infrastructure I proposed so that we can >>> continue that discussion. >> >> Again I'm deeply concerned and opposed to giving end users direct control >> over the IW value. I've had and seen too many cases of totally bogus >> "tuning" >> by cranking up random sysctls to insane values and then complaining about >> FreeBSD being slow compared to Linux (and then ditching FreeBSD). > > Sorry, but referring to unspecified cases of stupidity resulting in loss > of unquantified numbers of users as a reason against providing a > controlled mechanism to change a default system parameter in a > potentially harmful way is not a rational argument.
I do not subscribe to the idea of "Let's not make life of 98% of users better because 2% may do something stupid". I am revisiting this thread because at $work, we need to tweak initcwnd (other than 10) to see how it behaves but there is no easy way to tune it. (or am I missing something?) Can we please make initcwnd a sysctl tunable? cheers, Hiren _______________________________________________ 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"
