Hi Noah, Le 2021-01-07 16:12, Noah Meyerhans a écrit : > On Thu, Apr 23, 2020 at 03:34:06PM -0700, Matt Taggart wrote: > > #890343 was originally opened against systemd asking to install the upstream > > systemd sysctl.d/50-default.conf file that sets: > > > > net.core.default_qdisc = fq_codel > > > > As explained in #950701 (and the systemd debian changelog) the debian > > systemd maintainers felt that systemd in debian should not be changing > > kernel policies (and I agree). > > So #890343 was reassigned to linux to consider changing the default. > > > > fq_codel is better in every way than pfifo_fast and I am unaware of any > > reason why it would not be a better default. (but don't trust me, ask the > > kernel networking experts) > > > > Can we change it? > > I strongly agree that we should make this change for the bullseye > release. > > I'm looking into provding a patch to implement the switch to fq_codel by > default, but it appears to require something more than just a kernel > config change. I have tried the following with the 5.10 kernel from the > current sid branch: > > CONFIG_NET_SCH_FQ_CODEL=m > CONFIG_DEFAULT_FQ_CODEL=y > CONFIG_DEFAULT_NET_SCH="fq_codel" > > Then we don't see any change at all to the qdisc in use: > > admin@ip-10-0-0-162:~$ grep -i fq_codel /boot/config-$(uname -r) > CONFIG_NET_SCH_FQ_CODEL=m > CONFIG_DEFAULT_FQ_CODEL=y > CONFIG_DEFAULT_NET_SCH="fq_codel" > admin@ip-10-0-0-162:~$ /sbin/sysctl net.core.default_qdisc > net.core.default_qdisc = pfifo_fast > admin@ip-10-0-0-162:~$ tc qdisc show dev ens5 > qdisc mq 0: root > qdisc pfifo_fast 0: parent :2 bands 3 priomap 1 2 2 2 1 2 0 0 1 1 1 1 1 1 1 1 > qdisc pfifo_fast 0: parent :1 bands 3 priomap 1 2 2 2 1 2 0 0 1 1 1 1 1 1 1 1 > admin@ip-10-0-0-162:~$ ip link show dev ens5 > 2: ens5: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 9001 qdisc mq state UP mode > DEFAULT group default qlen 1000 > link/ether 02:47:e2:7c:be:ff brd ff:ff:ff:ff:ff:ff > altname enp0s5 > > If we statically link the fq_codel module into the kernel, then we see: > > admin@ip-10-0-0-162:~$ grep -i fq_codel /boot/config-$(uname -r) > CONFIG_NET_SCH_FQ_CODEL=y > CONFIG_DEFAULT_FQ_CODEL=y > CONFIG_DEFAULT_NET_SCH="fq_codel" > admin@ip-10-0-0-162:~$ /sbin/sysctl net.core.default_qdisc > net.core.default_qdisc = fq_codel > admin@ip-10-0-0-162:~$ /sbin/tc qdisc show dev ens5 > qdisc mq 0: root > qdisc fq_codel 0: parent :2 limit 10240p flows 1024 quantum 1514 target 5ms > interval 100ms memory_limit 32Mb ecn drop_batch 64 > qdisc fq_codel 0: parent :1 limit 10240p flows 1024 quantum 1514 target 5ms > interval 100ms memory_limit 32Mb ecn drop_batch 64 > admin@ip-10-0-0-162:~$ ip link show dev ens5 > 2: ens5: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 9001 qdisc mq state UP mode > DEFAULT group default qlen 1000 > link/ether 02:47:e2:7c:be:ff brd ff:ff:ff:ff:ff:ff > altname enp0s5 > > So in this case, we have fq_codel configured, but not as the root > qdisc for the interface. If we manually set it: > > admin@ip-10-0-0-162:~$ sudo /sbin/tc qdisc add root dev ens5 fq_codel > > Then we get the following configuration: > > admin@ip-10-0-0-162:~$ /sbin/tc qdisc show dev ens5 > qdisc fq_codel 8001: root refcnt 3 limit 10240p flows 1024 quantum 9015 > target 5ms interval 100ms memory_limit 32Mb ecn drop_batch 64 > admin@ip-10-0-0-162:~$ ip link show dev ens5 > 2: ens5: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 9001 qdisc fq_codel state UP > mode DEFAULT group default qlen 1000 > link/ether 02:47:e2:7c:be:ff brd ff:ff:ff:ff:ff:ff > altname enp0s5 > > I believe that this is what we want. Is that accurate? > > The recent thread at > https://www.mail-archive.com/netdev@vger.kernel.org/msg380410.html > also seems relevant.
I was about to start a thread on the debian-kernel ML about switching from pfifo_fast to FQ_Codel when I stumble across this bug report. My proposal would differ from yours though in that it would not touch the kernel configuration but would instead consist in patching procps to provide a configuration file (let's say default_qdisc.conf) to set the value of the net.core.default_qdisc variable to fq_codel via sysctl. This would allow to benefit from FQ_Codel without depending on a specific Linux version. Opinion? > noah Cheers, Vincent
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