On Mon, Jan 2, 2017 at 1:49 PM, Sedat Dilek <sedat.di...@gmail.com> wrote: > On Mon, Jan 2, 2017 at 7:17 PM, Neal Cardwell <ncardw...@google.com> wrote: >> On Mon, Jan 2, 2017 at 12:05 AM, Sedat Dilek <sedat.di...@gmail.com> wrote: >>> >>> Hi, >>> >>> I am trying to force the set of BBR congestion control as default. >>> My old linux-config uses CUBIC as default. >>> I want both BBR and CUBIC to be built but BBR shall be my default. >>> >>> I tried the below snippet. >>> >>> I refresh my new linux-config like this... >>> >>> $ MAKE="make V=1" ; COMPILER="mycompiler" ; MAKE_OPTS="CC=$COMPILER >>> HOSTCC=$COMPILER" ; yes "" | $MAKE $MAKE_OPTS oldconfig && $MAKE >>> $MAKE_OPTS silentoldconfig < /dev/null >>> >>> What am I doing wrong? >> >> Perhaps your build directory already has an old .config file that sets >> the DEFAULT_TCP_CONG to be "cubic", and your "make oldconfig" and >> "make silentoldconfig" are maintaining those lines from the old >> .config? >> >> If you want to start with your existing .config but then make BBR the >> default, then it might be simplest just to edit your .config directly: >> >> -CONFIG_DEFAULT_TCP_CONG="cubic" >> +CONFIG_DEFAULT_TCP_CONG="bbr" >> > > Just to clarify... > > I can have both TCP_CONG cubic and bbr built and switch for example via > sysctl?
Yes, you can set the default congestion control using sysctl, eg: sysctl net.ipv4.tcp_congestion_control=bbr And (as mentioned in the quick-start guide) on many Linux systems you can make this "sticky" after reboots with something like: sudo bash -c 'echo "net.ipv4.tcp_congestion_control=bbr" >> /etc/sysctl.conf' > Which tc version is required? > Here tc is from iproute (20121211-2~precise). > Is that enough? You should not need a particular version of tc to install "fq". In the BBR quick-start guide we recommend setting fq to be the default qdisc: sudo bash -c 'echo "net.core.default_qdisc=fq" >> /etc/sysctl.conf' But if that doesn't work in your environment, then I believe you should be able to install the fq qdisc with any version of tc, with something like: tc qdisc replace dev eth0 root fq You just won't be able to set or view configuration options. >> BTW, I presume you have seen the warning in the BBR commit message or >> tcp_bbr.c about ensuring that BBR is used with the "fq" qdisc: >> >> NOTE: BBR *must* be used with the fq qdisc ("man tc-fq") with pacing >> enabled, since pacing is integral to the BBR design and >> implementation. BBR without pacing would not function properly, and >> may incur unnecessary high packet loss rates. >> >> The BBR quick-start guide has some details about how to build and >> enable BBR and fq: >> >> https://github.com/google/bbr/blob/master/Documentation/bbr-quick-start.md >> > > Hmmm... > > From [1] Section "Further reading"... > > egrep '(CONFIG_TCP_CONG_BBR|CONFIG_NET_SCH_FQ)=' .config > > then you see exactly the following lines: > > CONFIG_TCP_CONG_BBR=y > CONFIG_NET_SCH_FQ=y > > Should CONFIG_TCP_CONG_BBR have a "select CONFIG_NET_SCH_FQ" in its Kconfig? > That would be safer. > > [1] https://github.com/google/bbr/blob/master/Documentation/bbr-quick-start.md That would be a little safer, but not sufficient (since the qdisc still has to be configured to be in the transmit path somewhere). thanks, neal