Message-ID: <DM6PR13MB309846DD4673636DF440000EC8BA9@DM6PR13MB3098.namprd13.prod.outlook.com>
Date:   Thu, 30 Jun 2022 14:59:14 +0000
From:   "U'ren, Aaron" <Aaron.U'ren@...y.com>
To:     Thorsten Leemhuis <regressions@...mhuis.info>
CC:     "McLean, Patrick" <Patrick.Mclean@...y.com>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        "netfilter-devel@...r.kernel.org" <netfilter-devel@...r.kernel.org>,
        "Brown, Russell" <Russell.Brown@...y.com>,
        "Rueger, Manuel" <manuel.rueger@...y.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "regressions@...ts.linux.dev" <regressions@...ts.linux.dev>,
        Florian Westphal <fw@...len.de>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Jozsef Kadlecsik <kadlec@...filter.org>
Subject: Re: Intermittent performance regression related to ipset between 5.10
 and 5.15

Thorsten / Jozsef -

Thanks for continuing to follow up! I'm sorry that this has moved so slow, it has taken us a bit to find the time to fully track this issue down, however, I think that we have figured out enough to make some more forward progress on this issue.

Jozsef, thanks for your insight into what is happening between those system calls. In regards to your question about wait/wound mutex debugging possibly being enabled, I can tell you that we definitely don't have that enabled on any of our regular machines. While we were debugging we did turn on quite a few debug options to help us try and track this issue down and it is very possible that the strace that was taken that started off this email was taken on a machine that did have that debug option enabled. Either way though, the root issue occurs on hosts that definitely do not have wait/wound mutex debugging enabled.

The good news is that we finally got one of our development environments into a state where we could reliably reproduce the performance issue across reboots. This was a win because it meant that we were able to do a full bisect of the kernel and were able to tell relatively quickly whether or not the issue was present in the test kernels.

After bisecting for 3 days, I have been able to narrow it down to a single commit: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=3976ca101990ca11ddf51f38bec7b86c19d0ca6f (netfilter: ipset: Expose the initval hash parameter to userspace)

I'm at a bit of a loss as to why this would cause such severe performance regressions, but I've proved it out multiple times now. I've even checked out a fresh version of the 5.15 kernel that we've been deploying with just this single commit reverted and found that the performance problems are completely resolved.

I'm hoping that maybe Jozsef will have some more insight into why this seemingly innocuous commit causes such larger performance issues for us? If you have any additional patches or other things that you would like us to test I will try to leave our environment in its current state for the next couple of days so that we can do so.

-Aaron

From: Thorsten Leemhuis <regressions@...mhuis.info>
Date: Monday, June 20, 2022 at 2:16 AM
To: U'ren, Aaron <Aaron.U'ren@...y.com>
Cc: McLean, Patrick <Patrick.Mclean@...y.com>, Pablo Neira Ayuso <pablo@...filter.org>, netfilter-devel@...r.kernel.org <netfilter-devel@...r.kernel.org>, Brown, Russell <Russell.Brown@...y.com>, Rueger, Manuel <manuel.rueger@...y.com>, linux-kernel@...r.kernel.org <linux-kernel@...r.kernel.org>, regressions@...ts.linux.dev <regressions@...ts.linux.dev>, Florian Westphal <fw@...len.de>, netdev@...r.kernel.org <netdev@...r.kernel.org>, Jozsef Kadlecsik <kadlec@...filter.org>
Subject: Re: Intermittent performance regression related to ipset between 5.10 and 5.15
On 31.05.22 09:41, Jozsef Kadlecsik wrote:
> On Mon, 30 May 2022, Thorsten Leemhuis wrote:
>> On 04.05.22 21:37, U'ren, Aaron wrote:
>>>  It’s good to have the confirmation about why iptables list/save 
>>> perform so many getsockopt() calls.
> 
> Every set lookups behind "iptables" needs two getsockopt() calls: you can 
> see them in the strace logs. The first one check the internal protocol 
> number of ipset and the second one verifies/gets the processed set (it's 
> an extension to iptables and therefore there's no internal state to save 
> the protocol version number).

Hi Aaron! Did any of the suggestions from Jozsef help to track down the
root case? I have this issue on the list of tracked regressions and
wonder what the status is. Or can I mark this as resolved?

Side note: this is not a "something breaks" regressions and it seems to
progress slowly, so I'm putting it on the backburner:

#regzbot backburner: performance regression where the culprit is hard to
track down

Ciao, Thorsten (wearing his 'the Linux kernel's regression tracker' hat)

P.S.: As the Linux kernel's regression tracker I deal with a lot of
reports and sometimes miss something important when writing mails like
this. If that's the case here, don't hesitate to tell me in a public
reply, it's in everyone's interest to set the public record straight.

>>>  In terms of providing more information to locate the source of the 
>>> slowdown, do you have any recommendations on what information would be 
>>> helpful?
>>>  The only thing that I was able to think of was doing a git bisect on 
>>> it, but that’s a pretty large range, and the problem isn’t always 100% 
>>> reproducible. It seems like something about the state of the system 
>>> needs to trigger the issue. So that approach seemed non-optimal.
>>>  I’m reasonably certain that if we took enough of our machines back to 
>>> 5.15.16 we could get some of them to evidence the problem again. If we 
>>> reproduced the problem, what types of diagnostics or debug could we 
>>> give you to help further track down this issue?
> 
> In your strace log
> 
> 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 <0.1$
> 0.109456 close(4)                  = 0 <0.000022>
> 
> the only things which happen in the second sockopt function are to lock 
> the NFNL_SUBSYS_IPSET mutex, walk the array of the sets, compare the 
> setname, save the result in the case of a match and unlock the mutex. 
> Nothing complicated, no deep, multi-level function calls. Just a few line 
> of codes which haven't changed.
> 
> The only thing which can slow down the processing is the mutex handling. 
> Don't you have accidentally wait/wound mutex debugging enabled in the 
> kernel? If not, then bisecting the mutex related patches might help.
> 
> You wrote that flushing tables or ipsets didn't seem to help. That 
> literally meant flushing i.e. the sets were emptied but not destroyed? Did 
> you try both destroying or flushing?
> 
>> Jozsef, I still have this issue on my list of tracked regressions and it
>> looks like nothing happens since above mail (or did I miss it?). Could
>> you maybe provide some guidance to Aaron to get us all closer to the
>> root of the problem?
> 
> I really hope it's an accidentally enabled debugging option in the kernel. 
> Otherwise bisecting could help to uncover the issue.
> 
> Best regards,
> Jozsef
> 
>> P.S.: As the Linux kernel's regression tracker I deal with a lot of
>> reports and sometimes miss something important when writing mails like
>> this. If that's the case here, don't hesitate to tell me in a public
>> reply, it's in everyone's interest to set the public record straight.
>>
>>
>>> From: Thorsten Leemhuis <regressions@...mhuis.info>
>>> Date: Wednesday, May 4, 2022 at 8:15 AM
>>> To: McLean, Patrick <Patrick.Mclean@...y.com>
>>> Cc: Pablo Neira Ayuso <pablo@...filter.org>, netfilter-devel@...r.kernel.org <netfilter-devel@...r.kernel.org>, U'ren, Aaron <Aaron.U'ren@...y.com>, Brown, Russell <Russell.Brown@...y.com>, Rueger, Manuel <manuel.rueger@...y.com>, linux-kernel@...r.kernel.org <linux-kernel@...r.kernel.org>, regressions@...ts.linux.dev <regressions@...ts.linux.dev>, Florian Westphal <fw@...len.de>, netdev@...r.kernel.org <netdev@...r.kernel.org>, Jozsef Kadlecsik <kadlec@...filter.org>
>>> Subject: Re: Intermittent performance regression related to ipset between 5.10 and 5.15
>>> Hi, this is your Linux kernel regression tracker. Top-posting for once,
>>> to make this easily accessible to everyone.
>>>
>>> Patrick, did you see the comment from Jozsef? Are you having trouble
>>> providing additional data or what's the status here from your side? Or
>>> is that something we can forget?
>>>
>>> Ciao, Thorsten
>>>
>>> #regzbot poke
>>>
>>> On 11.04.22 13:47, Jozsef Kadlecsik wrote:
>>>> 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://urldefense.com/v3/__https:/www.kernel.org/doc/html/latest/admin-guide/reporting-issues.html__;!!JmoZiZGBv3RvKRSx!9uRzPn01pFuoHMQj2ZsxlSeY6NoNdYH6BxvEi_JHC4sZoqDTp8X2ZYrIRtIOhN7RM0PtxYLq4NIe9g0hJqZVpZdwVIY5$ 
>>>>>>
>>>>>> 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.
>>>>>>
>>>>>
>>>>
>>>> -
>>>> E-mail  : kadlec@...ckhole.kfki.hu, kadlecsik.jozsef@...ner.hu
>>>> PGP key : https://urldefense.com/v3/__https:/wigner.hu/*kadlec/pgp_public_key.txt__;fg!!JmoZiZGBv3RvKRSx!9uRzPn01pFuoHMQj2ZsxlSeY6NoNdYH6BxvEi_JHC4sZoqDTp8X2ZYrIRtIOhN7RM0PtxYLq4NIe9g0hJqZVpRHTvk29$ 
>>>> Address : Wigner Research Centre for Physics
>>>>            H-1525 Budapest 114, POB. 49, Hungary
>>>
>>>
>>
> 
> -
> E-mail  : kadlec@...ckhole.kfki.hu, kadlecsik.jozsef@...ner.hu
> PGP key : https://urldefense.com/v3/__https:/wigner.hu/*kadlec/pgp_public_key.txt__;fg!!JmoZiZGBv3RvKRSx!4YE_vzTwH11tLmht_mqRbx-shqc9cGCmFtFWueoKCMt0uJaqWdFzheT3KdEC-7cAqnf0Gnu82USHlLemKtf5x5I6KaHM$ 
> Address : Wigner Research Centre for Physics
>           H-1525 Budapest 114, POB. 49, Hungary

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