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Diffstat (limited to '_drafts/bird-cpu-usage.md')
| -rw-r--r-- | _drafts/bird-cpu-usage.md | 64 |
1 files changed, 47 insertions, 17 deletions
diff --git a/_drafts/bird-cpu-usage.md b/_drafts/bird-cpu-usage.md index 36bad4e..c0fa5b7 100644 --- a/_drafts/bird-cpu-usage.md +++ b/_drafts/bird-cpu-usage.md @@ -6,6 +6,19 @@ categories: tech lang: en --- +**Preface**: This is kind of a "bug hunt log". I extensively posted on Mastodon +about it, but wanted to keep the progress in writing as well. This might lead +like random rambling in some parts, because I edited and rearranged the +paragraphs of this post a few times. Sorry for that. + +**Preface 2**: Starting point: In September 2024 I upgraded to bird2 +`2.15.1-1~bpo12+1` - probably a self-built backport of mine. This, I "had to +to", since I wanted the Babel metrics measurement, which is not present in +Debian stable (`2.0.12-7`). Yeah, I won't complain. For 99 % of the stuff I do, +Debian stable is *perfect*. I want a server without regularly breaking things, +after all. Only recently (2015-01-07), I added the bird / network.cz repos and +installed bird2 from there. + Several times already, I noticed this in my Munin monitoring: {% image @@ -17,7 +30,7 @@ I found it strange, but had no time to inspect further. Recently, I tried to investigate what happens on the server there. htop showed high CPU usage for both bird and dnsmasq (always together) in these times. -Fuming a bit, I went with a brute-force approach: +Fuming (angry) a bit, I went with a brute-force approach: ``` #!/bin/bash @@ -59,7 +72,7 @@ while true; do # Send alert email (echo "$BODY"; ps -e -o %cpu,%mem,cmd --sort pcpu | tail) | mail -s "$SUBJECT" "$MAIL_TO" - # Reboot the server + # Reboot the server - room for improvement # systemctl stop bird # systemctl start bird $REBOOT_CMD @@ -81,8 +94,8 @@ Specifically, the output of ps 37.4 0.0 /usr/sbin/dnsmasq -x /run/dnsmasq/dnsmasq.pid -u dnsmasq -7 /etc/dnsmasq.d,.dpkg-dist,.dpkg-old,.dpkg-new,.bak --local-service --trust-anchor=.,20326,8,2,e06d44b80b8f1d39a95c0b0d7c65d08458e880409bbc683457104237c7f8ec8d ``` -confirmed the suspicion - although the "percentage" is a bit weird. From the -manpage: +confirmed the quick look at htop - although the "percentage" is a bit weird. +From the manpage: > Currently, it is the CPU time used divided by the time the process has been > running (cputime/realtime ratio), expressed as a percentage. @@ -96,45 +109,62 @@ debug symbols](https://wiki.debian.org/HowToGetABacktrace) - it doesn't for dnsmasq (yet) in bookworm. Luckily, the nice people at labs.nic.cz provide a dbgsym package in their Bird(2) Debian repository. +Aside, the script above could benefit from some improvements, instead of +rebooting, I could actually record and strace and perf when this happens, and +only then reboot / restart the service. + Now, stracing dnsmasq (when "idle") reveals some recvmsg of type `RTM_NEWROUTE`. I have *no idea* why dnsmasq would need that. But I already *assume* the high CPU usage occurs when Bird exports lots of routes to the -kernel. +kernel. *I have no hecking clue why dnsmasq would need to use the CPU at the +same time. If someone can enlighten me, **please** message me.* Also, in journalctl, I see lots of the infamous `Kernel dropped some netlink messages, will resync on next scan.` messages at times - the message apparently nobody has a solution to, and even though there are mailing list posts telling to sysctl `net.core.rmem_default`, I doesn't seem to yield a solution. -[1] At least when I want to see the binaries function names. Kernel symbols -seem to show up fine. +I actually did a `perf record` of bird when the CPU usage was high, and I saw +that `rt_event` was running 33% of the time. I don't know what to make of that. So… step-by-step? I have both DN42 and clearnet bird running on this VPS, in parallel. So maybe start by disabling one of these? Or, I have a better idea, -keep it enabled, and disable all protocols! (`birdc disable \"*\"`). - -That helped, until midnight. When suddenly the CPU went up again. WTF? Let's -have a look at `birdc s p`. All protocols up. Huh!?!? +keep it enabled, and disable all protocols! (`birdc disable \"*\"`). That +helped, until midnight. When suddenly the CPU went up again. WTF? Let's have a +look at `birdc s p`. All protocols up. Huh!?!? Let's investigate further: * Oooo, log rotation happens at midnight * Fuck, I specified the same log files for both bird's -Well, log rotation. Which I added manually. This does a `birdc configure` -afterward. Which means the protocols go up again, because I disabled them on -the command line, not in the config. +Well, log rotation. Which I added myself. This does a `birdc configure` +afterward. Which means the protocols go up again, because I disabled them on the +command line, not in the config. Ungh. Okay, this is getting really ugly. `systemctl disable --now bird-clear`. Now let's run this for a few days... -That seem to have helped. I not decided to edit the clearnet config and disable +That seem to have helped. I now decided to edit the clearnet config and disable all "external" protocols (to IXPs), keeping Babel, RPKI, and IBGP enabled. Immediately after starting bird-clearnet, the CPU usage went up again. To be expected, for the initial sync. But it kept being high. So, I disabled the RPKI protocols as well and... suddenly, the CPU usage is down??? -I actually did a `perf record` of bird when the CPU usage was high, and I saw -that `rt_event` was running 33% of the time. I don't know what to make of that. +(2025-01-09) So, now, the RPKI stuff... I saw that the connection to one of my +RPKI servers wouldn't work (Fort Validator), and Fort complained about `Bad RTR +version: 2`. The [Bird +docs](https://bird.network.cz/?get_doc&v=20&f=bird-6.html) mention a `max +version` option, and with that, the connection worked. And the CPU usage was +down. *However*, this was not "the root issue". This option is only present +since bird 2.16, which I only installed on 2025-01-07 [2]. And I had the CPU +problems back in November last year! So this is "something completely +different", it appears. I currently have the BGP sessions to virtual IXPs +disabled, and will run it like this for a few days. The average load is 0.4. +Still too high, compared to my other VPS. +[1] At least when I want to see the binaries function names. Kernel symbols +seem to show up fine. \ +[2] Which is pretty annoying, when you chase one bug, you change something in +your config, and then something else breaks. That's on me. |