Re: Intermittent performance regression related to ipset between 5.10 and 5.15

[Jozsef Kadlecsik <kadlec@netfilter.org>]

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Hi,

On Mon, 11 Apr 2022, Thorsten Leemhuis wrote:

> On 16.03.22 10:17, Thorsten Leemhuis wrote:
> > [TLDR: I'm adding the regression report below to regzbot, the Linux
> > kernel regression tracking bot; all text you find below is compiled from
> > a few templates paragraphs you might have encountered already already
> > from similar mails.]
> > 
> > On 16.03.22 00:15, McLean, Patrick wrote:
>
> >> When we upgraded from the 5.10 (5.10.61) series to the 5.15 (5.15.16) 
> >> series, we encountered an intermittent performance regression that 
> >> appears to be related to iptables / ipset. This regression was 
> >> noticed on Kubernetes hosts that run kube-router and experience a 
> >> high amount of churn to both iptables and ipsets. Specifically, when 
> >> we run the nftables (iptables-1.8.7 / nftables-1.0.0) iptables 
> >> wrapper xtables-nft-multi on the 5.15 series kernel, we end up 
> >> getting extremely laggy response times when iptables attempts to 
> >> lookup information on the ipsets that are used in the iptables 
> >> definition. This issue isn’t reproducible on all hosts. However, our 
> >> experience has been that across a fleet of ~50 hosts we experienced 
> >> this issue on ~40% of the hosts. When the problem evidences, the time 
> >> that it takes to run unrestricted iptables list commands like 
> >> iptables -L or iptables-save gradually increases over the course of 
> >> about 1 - 2 hours. Growing from less than a second to run, to takin
>  g sometimes over 2 minutes to run. After that 2 hour mark it seems to 
>  plateau and not grow any longer. Flushing tables or ipsets doesn’t seem 
>  to have any affect on the issue. However, rebooting the host does reset 
>  the issue. Occasionally, a machine that was evidencing the problem may 
>  no longer evidence it after being rebooted.
> >>
> >> We did try to debug this to find a root cause, but ultimately ran 
> >> short on time. We were not able to perform a set of bisects to 
> >> hopefully narrow down the issue as the problem isn’t consistently 
> >> reproducible. We were able to get some straces where it appears that 
> >> most of the time is spent on getsockopt() operations. It appears that 
> >> during iptables operations, it attempts to do some work to resolve 
> >> the ipsets that are linked to the iptables definitions (perhaps 
> >> getting the names of the ipsets themselves?). Slowly that getsockopt 
> >> request takes more and more time on affected hosts. Here is an 
> >> example strace of the operation in question:

Yes, iptables list/save have to get the names of the referenced sets and 
that is performed via getsockopt() calls.

I went through all of the ipset related patches between 5.10.6 (copy&paste 
error but just the range is larger) and 5.15.16 and as far as I see none 
of them can be responsible for the regression. More data is required to 
locate the source of the slowdown.

Best regards,
Jozsef

> >>
> >> 0.000074 newfstatat(AT_FDCWD, "/etc/nsswitch.conf", {st_mode=S_IFREG|0644, st_size=539, ...}, 0) = 0 <0.000017>
> >> 0.000064 openat(AT_FDCWD, "/var/db/protocols.db", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory) <0.000017>
> >> 0.000057 openat(AT_FDCWD, "/etc/protocols", O_RDONLY|O_CLOEXEC) = 4 <0.000013>
> >> 0.000034 newfstatat(4, "", {st_mode=S_IFREG|0644, st_size=6108, ...}, AT_EMPTY_PATH) = 0 <0.000009>
> >> 0.000032 lseek(4, 0, SEEK_SET)     = 0 <0.000008>
> >> 0.000025 read(4, "# /etc/protocols\n#\n# Internet (I"..., 4096) = 4096 <0.000010>
> >> 0.000036 close(4)                  = 0 <0.000008>
> >> 0.000028 write(1, "ANGME7BF25 - [0:0]\n:KUBE-POD-FW-"..., 4096) = 4096 <0.000028>
> >> 0.000049 socket(AF_INET, SOCK_RAW, IPPROTO_RAW) = 4 <0.000015>
> >> 0.000032 fcntl(4, F_SETFD, FD_CLOEXEC) = 0 <0.000008>
> >> 0.000024 getsockopt(4, SOL_IP, 0x53 /* IP_??? */, "\0\1\0\0\7\0\0\0", [8]) = 0 <0.000024>
> >> 0.000046 getsockopt(4, SOL_IP, 0x53 /* IP_??? */, "\7\0\0\0\7\0\0\0KUBE-DST-VBH27M7NWLDOZIE"..., [40]) = 0 <0.109384>
> >> 0.109456 close(4)                  = 0 <0.000022>
> >>
> >> On a host that is not evidencing the performance regression we 
> >> normally see that operation take ~ 0.00001 as opposed to 
> >> 0.109384.Additionally, hosts that were evidencing the problem we also 
> >> saw high lock times with `klockstat` (unfortunately at the time we 
> >> did not know about or run echo "0" > /proc/sys/kernel/kptr_restrict 
> >> to get the callers of the below commands).
> >>
> >> klockstat -i 5 -n 10 (on a host experiencing the problem)
> >> Caller   Avg Hold  Count   Max hold Total hold
> >> b'[unknown]'  118490772     83  179899470 9834734132
> >> b'[unknown]'  118416941     83  179850047 9828606138
> >> # or somewhere later while iptables -vnL was running:
> >> Caller   Avg Hold  Count   Max hold Total hold
> >> b'[unknown]'  496466236     46 17919955720 22837446860
> >> b'[unknown]'  496391064     46 17919893843 22833988950
> >>
> >> klockstat -i 5 -n 10 (on a host not experiencing the problem)
> >> Caller   Avg Hold  Count   Max hold Total hold
> >> b'[unknown]'     120316   1510   85537797  181677885
> >> b'[unknown]'    7119070     24   85527251  170857690
> > 
> > Hi, this is your Linux kernel regression tracker.
> > 
> > Thanks for the report.
> > 
> > CCing the regression mailing list, as it should be in the loop for all
> > regressions, as explained here:
> > https://www.kernel.org/doc/html/latest/admin-guide/reporting-issues.html
> > 
> > To be sure below issue doesn't fall through the cracks unnoticed, I'm
> > adding it to regzbot, my Linux kernel regression tracking bot:
> > 
> > #regzbot ^introduced v5.10..v5.15
> > #regzbot title net: netfilter: Intermittent performance regression
> > related to ipset
> > #regzbot ignore-activity
> > 
> > If it turns out this isn't a regression, free free to remove it from the
> > tracking by sending a reply to this thread containing a paragraph like
> > "#regzbot invalid: reason why this is invalid" (without the quotes).
> > 
> > Reminder for developers: when fixing the issue, please add a 'Link:'
> > tags pointing to the report (the mail quoted above) using
> > lore.kernel.org/r/, as explained in
> > 'Documentation/process/submitting-patches.rst' and
> > 'Documentation/process/5.Posting.rst'. Regzbot needs them to
> > automatically connect reports with fixes, but they are useful in
> > general, too.
> > 
> > I'm sending this to everyone that got the initial report, to make
> > everyone aware of the tracking. I also hope that messages like this
> > motivate people to directly get at least the regression mailing list and
> > ideally even regzbot involved when dealing with regressions, as messages
> > like this wouldn't be needed then. And don't worry, if I need to send
> > other mails regarding this regression only relevant for regzbot I'll
> > send them to the regressions lists only (with a tag in the subject so
> > people can filter them away). With a bit of luck no such messages will
> > be needed anyway.
> > 
> > Ciao, Thorsten (wearing his 'the Linux kernel's regression tracker' hat)
> > 
> > P.S.: As the Linux kernel's regression tracker I'm getting a lot of
> > reports on my table. I can only look briefly into most of them and lack
> > knowledge about most of the areas they concern. I thus unfortunately
> > will sometimes get things wrong or miss something important. I hope
> > that's not the case here; if you think it is, don't hesitate to tell me
> > in a public reply, it's in everyone's interest to set the public record
> > straight.
> > 
> 

-
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