Thank you all for helping! I wasn't expecting such a large number of replies!

I ended up partially solving the issue with a different approach. 
Modifying the size of the UDP Buffer did not reveal any improvement. However, modifying the memory management did improve a lot: from 330 CPS to 1800 CPS in stateful mode. 
So, starting kamailio with the following command:

 kamailio -M 256 -m 128 -f <script.cfg> 

did the trick! And the VM is still running with 6 vCPU.

Still very far from the test results described in https://www.kamailio.org/docs/openser-performance-tests/#tm-tests-c but a lot better and meets our requirements

Thanks guys for your help! Greatly appreciated!
    

Sérgio Charrua


On Sun, Mar 24, 2024 at 4:28 PM Alex Balashov via sr-users <sr-users@lists.kamailio.org> wrote:
Not really related to the ongoing discussion, but:

Going to that kind of CPS might exceed the natural limits of all but the most exquisitely tuned execution environments. It probably wouldn't work at all on the average moderately oversubscribed public cloud VM, even a generously resourced one.

Once you get to that point, you might be better off just scaling horizontally.

-- Alex

> On Mar 23, 2024, at 11:26 PM, Ovidiu Sas <osas@voipembedded.com> wrote:
>
> It all depends on the hardware, but I noticed that after you pass 3-4k cps you run into this kind of issues.
>
> - ovidiu
>
> On Sat, Mar 23, 2024 at 22:11 Alex Balashov via sr-users <sr-users@lists.kamailio.org> wrote:
>
> > On Mar 23, 2024, at 9:30 PM, Ovidiu Sas <osas@voipembedded.com> wrote:
> >
> > In the end, we agree with each other and my feeling is that we are repeating the same concept.
>
> Yeah, I think that's mostly right.
>
> > In most of my deployments I don’t need to mess with the udp queue size.
> > For high cps traffic, from my experience, it’s a must.
>
> Although I don't deal with very high-CPS deployments (500-1000 CPS) much these days, I used to, and my experiences there led me to the diametrically opposite conclusion: one should never increase the UDP queue size, and if you find yourself doing that, you're doing something wrong, _except_ in the occasional burst case we discussed.
>
> You can be absolutely sure that when I first encountered the problem, my first impulse was to increase the receive queue as high as it will go, then, gradually, to a lesser extent. I ultimately found that the proper amount by which to raise it is 0. ;)
>
> -- Alex
>
> --
> Alex Balashov
> Principal Consultant
> Evariste Systems LLC
> Web: https://evaristesys.com
> Tel: +1-706-510-6800
>
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--
Alex Balashov
Principal Consultant
Evariste Systems LLC
Web: https://evaristesys.com
Tel: +1-706-510-6800

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