Playing with fq_codel in 2.4

tman222

@uptownvagrant said in Playing with fq_codel in 2.4:

Looking at the examples in the paper, I'm wondering why the Codel AQM is selected in the pfSense WebUI in the August 2018 hangout? Per the FQ-CoDel examples in the paper above, it does not seem appropriate and removing Codel as the AQM from the pipe and queue removes the "flowset busy" error @mattund mentioned 4 months ago. @dtaht this is why I was stating codel+fq-codel - when I first learned about FQ-CoDel being added to pfSense 2.4.4, it was in the hangout video which it instructs to choose Codel as the AQM.

I have wondered the same as well (if you look up a few posts I shared some thoughts on this based on my current understanding of Dummynet and Limiters). In most situations, the scheduler chosen is just that - a scheduler only. In that case controlling the traffic flowing to the scheduler in the queue(s) makes sense to me. However, fq_codel combines scheduling and AQM into one, so having Codel on the input queue(s) seems a bit redundant to me. Now having said that, I currently have both enabled and it provides the best performance in my case. I'm still trying to figure out exactly as to why, but it might be because I'm trying to push a lot of packets from a 10Gbit LAN link into a 1Gbit WAN link and the additional AQM helps keeps things orderly.

I would be very interested to see some comparisons of Codel + fq_codel vs. just fq_codel as I do wonder at which point it actually starts to make a difference vs. just using additional processing without any real benefit.

strangegopher

Just wanted to report that my ipq806x based router tp-link archer c2600 could only do about 85-119 mbps download with qos on but was able to max out my speed with qos off. Guess I'll be returning the router.

zwck

@dtaht said in Playing with fq_codel in 2.4:

flent has now been packaged up and made available for freebsd.

https://github.com/tohojo/flent/commit/c928c03a301258c26c7d045c74ecce6dfeaa3d5a

This has not gone unnoticed, it took me while to take a look!
In order to use the flent pkg you most likely have to be on the latest pkg train (often its the quarterly branch). For the FreeNAS users:

Create the file /usr/local/etc/pkg/repos/FreeBSD.conf as noted but override the URL instead of disabling the repository:
Code:

FreeBSD: {
  url: "pkg+http://pkg.FreeBSD.org/${ABI}/latest"
}

then in shell

pkg update
pkg install flent
# first test
flent rrul -p all_scaled -l 60 -H flent-london.bufferbloat.net -t no_shaper -o RRUL_no_shaper.png

cheers!

strangegopher

@mattund wouldn't there be a security issue with wan facing bridge interfaces and lan facing management interface on the same machine?

mattund

@strangegopher

Eh, it's an unaddressed layer 2 bridge and just passes the traffic straight through. It won't route to the internal net from the external side unless it's through pfSense. On the internal side, I guess, but this is all home usage. I think it's ultimately up to the implementer to decide how they best want to manage it, my choice to use that management interface doesn't impact the functionality of what it accomplishes (although, like dtaht said, you lose per-host FQ if you neglect the NAT to pfSense like I am, but I am OK with that)

I do recommend disabling IPv6 on the machine's "default" interfaces (everything but eth0) though: net.ipv6.conf.default.disable_ipv6=1, so it will only accept forward Layer2 stuff, and just double-check ip route, ip -6 route are all via eth0.... let me know if there's something I'm missing.

strangegopher

@mattund I see, just checking if it was an issue.

Rasool

Hello everyone,

I am the developer of Dummynet AQM (CoDel/PIE/FQ-CoDel and FQ-PIE). I have read part of this very long interesting thread and I can see some of you have the "config_aqm Unable to configure flowset, flowset busy!" error.
That error tells you that you are trying to reconfigure a flowset (pipe or queue) while there is an actual traffic uses that flowset (it has an active scheduler). I prevent reconfiguring an active flowset because I had some difficulties freeing/reallocating individual AQM (CoDel and PIE) memory space (as well as timeout function used by PIE which can cause a kernel panic). Definitely, the issue can be solved with some work but I hadn't (and I still don't have) enough time to fix that issue.
However, there is an easy workaround to avoid this error. If you make sure that there's no traffic passes through the pipe/queue that you want to reconfigure, then you can reconfigure the pipe/queue without problems. To achieve that you can use "skipto" action (in ipfw) to skip the rules that include the pipes/queues you would like to configure. Here is an example:

00010  70451180  71665155748 skipto 65534 ip from any to any
00100    188029      9852488 pipe 1 ip from 172.16.10.0/24 to 172.16.11.0/24 out
65534 165525594 168354591831 allow ip from any to any
65535         0            0 deny ip from any to any

Now, pipe 1 can be reconfigured without problems.

ipfw pipe 1 config bw 10mbit/s codel

Please note that sometimes you should wait for a short time (based on net.inet.ip.dummynet.expire sysctl) to allow queues/schedulers to drain before reconfiguring the pipe/queue.
For scheduler/AQM cases (i.e. fq_codel and fq_pie), you have to skip the queues instead of pipes.

I hope this workaround works for you. Please let me know if you still have issues and I will try to do my best to provide solutions.

Regards,
Rasool Al-Saadi

Rasool

Additionally, I cannot understand what is the purpose of using Codel + fq_codel?
I want to clarify some dummynet/AQM internals to understand what does Codel + fq_codel mean. (all figures are from [http://caia.swin.edu.au/reports/160708A/CAIA-TR-160708A.pdf]).

CoDel and PIE:
In a simple setup, when a new dummynet pipe is configured, a queue (Droptail queue), two schedulers (FIFO and WF2Q+) and a link (traffic shaper and delay emulation) are created. The queue is connected to FIFO scheduler and the scheduler is connected to a link. If we reconfigure the pipe, dummynet will configure the queue and the link.

For example, the following command will set traffic shaping to 10mbit/s for the link and set Codel AQM (instead of droptail) to be used with the queue. Note that CoDel and PIE can be used to manage the queue (not the pipe).

ipfw pipe 1 config bw 10mbit/s codel

fq_codel and fq_pie:
fq_codel and fq_pie algorithms are implemented as dummynet schedulers and they have internal sub-queues as shown in the figure below.

We need a queue, a scheduler and a link to configure fq_codel/fq_pie. The queue is not "really" used to buffer packets but just to add it the ipfw rules. All packets are stored in fq_codel/fq_pie sub-queues directly. The scheduler is full fq_codel and fq_pie implementation (sub-queue buffers, DDR and codel/pie). The link is a normal dummynet link (traffic shaper).
We have to configure a pipe to create a link since we cannot configure a link alone (according to my knowledge).
Example:

ipfw pipe 1 config  bw 800Mb
ipfw sched 1 config pipe 1 type fq_codel target 5ms interval 100ms quantum 1514 limit 1024 flows 1024 ecn
ipfw queue 1 config pipe 1 sched 1

Then we add queue 1 to ipfw rules (in my case)

 ipfw add 100 queue 1 ip from 172.16.10.0/24 to 172.16.11.0/24 out

Now, Codel + fq_codel is basically just fq_codel if the firewall is configured using the method above.

Finally, I saw some configurations use queue with "mask" option and Codel. That is useful if you want to try different scheduling algorithms with codel/pie and flow separation to produce something similar to fq_codel. For example, you use that method to produce WF2Q+_codel, qfq_pie, qfq_codel, ... etc. This method produces similar results to fq_codel in general but not exactly the same (no priority for new flows for example).

Hopefully, the explanation above was clear and useful.

Regards,
Rasool

strangegopher

@Rasool can this be done in current implementation in the UI? or does @mattund need to get involved.

Rasool

@strangegopher Unfortunately, I cannot help with regard to the UI. To be honest, I haven't used pfsense before and I use only ipfw/dummynet CLI to configure my router/firewall.

strangegopher

@Rasool I was able to get it working with first creating a random limiter and setting that limiter in firewall pipe rule and then creating this shellcmd and rebooting.

0_1541684169624_Annotation 2018-11-08 053512.jpg

edit: actually setting Queue to droptail in settings does the same thing. ignore my last comment.

Rasool

@strangegopher Excellent work!
I installed pfSense and was able to setup fq_codel correctly (without CoDel) using just the WebUI. Here are the steps:

1- Create "out" limiter

Tick Enable
Name: pipe_out
Set the bandwidth
Queue Management Algorithm: Tail Drop
Scheduler: FQ_CODEL

2- Add new Queue

Tick "Enable"
Name: queue_out
Queue Management Algorithm: Tail Drop
Save

3- Create "in" limiter

Tick Enable
Name: pipe_in
Set the bandwidth
Queue Management Algorithm: Tail Drop
Scheduler: FQ_CODEL

4- Add new Queue

Tick "Enable"
Name: queue_in
Queue Management Algorithm: Tail Drop
Save

5- Add limiter in firewall rule

Configure floating rule (as normal)
In / Out pipe: queue_in / queue_out

I believe these steps prevent "config_aqm Unable to configure flowset, flowset busy!" error and no need for rebooting pfSense.

Could you please test the above setup?

strangegopher

@rasool Yes!!! That is exactly what I did and I no longer see those errors even when my bandwidth is being used.

uptownVagrant

@rasool

This is what I found too. Big thanks to you for implementing these schedulers into ipfw/dummynet!

@uptownvagrant said in Playing with fq_codel in 2.4:

So I read this paper Dummynet AQM v0.1 – CoDel and FQ-CoDel for FreeBSD’s ipfw/dummynet framework

The paper is written by the folks that implemented Codel and FQ-CoDel into FreeBSD ipfw/dummynet. I know @dtaht knows this because he reviewed the source and there is correspondence between them and he back in the day. I'm just catching up - thanks for your patience.

Looking at the examples in the paper, I'm wondering why the Codel AQM is selected in the pfSense WebUI in the August 2018 hangout? Per the FQ-CoDel examples in the paper above, it does not seem appropriate and removing Codel as the AQM from the pipe and queue removes the "flowset busy" error @mattund mentioned 4 months ago. @dtaht this is why I was stating codel+fq-codel - when I first learned about FQ-CoDel being added to pfSense 2.4.4, it was in the hangout video which it instructs to choose Codel as the AQM.

Concerning buckets and CPU utlization, I played with net.inet.ip.dummynet.hash_size which is the closest thing I could find to what you were explaining - pfSense defaults to 256 and I doubled the value on each flent rrul test up to 16384. I had to use sysctl -w net.inet.ip.dummynet.hash_size=$value on the fly in the console because /etc/inc/shaper.inc overwrites the setting to 256 any time you make a change to the limiters. I did not find setting this above 256 to provide real value.

So, unfortunately I haven't made much progress...

tman222

Hi @rasool - Welcome! It's great to see you joining the discussion.

I'm very glad you were able to confirm the proper setup. I had postulated something similar a few post back up in this thread based on what I had read about Limiters/Dummynet:

https://forum.netgate.com/topic/112527/playing-with-fq_codel-in-2-4/635

Here's one interesting thing though (and a question that I'm still trying to answer): In my case I have a 10Gbit LAN feeding into a 1Gbit WAN link. If I enable Codel on the limiter's child queues I see slightly better performance than just enabling fq_codel and leaving AQM alone on the queues (i.e. just going with the default Tail Drop).

Now, is it the case that with Codel enabled on the child queues, some of the packets being received would already be dropped before reaching the fq_codel scheduler and its own set of queues? In other words there are two stages of AQM occurring? Or is Codel AQM on the child queues ignored when fq_codel is enabled?

I definitely agree that it is not necessary to have Codel enabled on child queues since fq_codel handles the AQM with its own set of queues. However, could adding the Codel to child queues help when dealing with high speed (high pps) networks with a slower uplink? Or am I just creating additional CPU overhead and no benefit?

Thanks in advance for the help and clarification, I really appreciate it.

Rasool

@uptownvagrant
Sorry, I missed that post :( Anyways, if you use the setup above without dynamic flows (without using mask option), I don't think change net.inet.ip.dummynet.hash_size can improve CPU utilization when FQ-CoDel is used since Dummynet fq_codel implementation creates and manages its own sub-queues.

Rasool

@tman222 said in Playing with fq_codel in 2.4:

I'm very glad you were able to confirm the proper setup. I had postulated something similar a few post back up in this thread based on what I had read about Limiters/Dummynet:
https://forum.netgate.com/topic/112527/playing-with-fq_codel-in-2-4/635

You provided very nice information in that post. Actually, I tried your RR+Codel setup a long time ago to confirm a specific behaviour I saw with our fq_codel implementation. Regarding the differences to fq_codel (in addition to the quantum value you mentioned and regardless of the internal implementation differences), FQ-CoDel has two groups of sub-queues. One group for new (and very short-life like a DNS query) flows and other for old flows. New flows sub-queue has higher priority than old flows. This prioritisation improves network response (RFC8290 explains that very clearly).

@tman222 said in Playing with fq_codel in 2.4:

Here's one interesting thing though (and a question that I'm still trying to answer): In my case I have a 10Gbit LAN feeding into a 1Gbit WAN link. If I enable Codel on the limiter's child queues I see slightly better performance than just enabling fq_codel and leaving AQM alone on the queues (i.e. just going with the default Tail Drop).

That's so weird. Choosing CoDel or Tail Drop with fq_codel should not change the performance at all. In fact, Tail Drop or CoDel enqueue/dequeue code is not be executed at all when fq_codel scheduler is configured (fq_codel has sperate enqueue/dequeue functions).

@tman222 said in Playing with fq_codel in 2.4:

Now, is it the case that with Codel enabled on the child queues, some of the packets being received would already be dropped before reaching the fq_codel scheduler and its own set of queues? In other words there are two stages of AQM occurring? Or is Codel AQM on the child queues ignored when fq_codel is enabled?

The answer is Codel AQM on the child queues ignored when fq_codel is enabled. So, CoDel will not drop any packet in this setup and the buffer space of the child queue will not be used to store packets at all.

@tman222 said in Playing with fq_codel in 2.4:

I definitely agree that it is not necessary to have Codel enabled on child queues since fq_codel handles the AQM with its own set of queues. However, could adding the Codel to child queues help when dealing with high speed (high pps) networks with a slower uplink? Or am I just creating additional CPU overhead and no benefit?

As you mentioned, fq_codel uses its own queues. These queues are accessible only by fq_codel instances. As mentioned in ipfw(8) man page, you can configure the number of these queues using fq_codel flows parameter. I don't think you are creating additional CPU overhead by enabling CoDel.

Sorry if you mentioned that in your early post (so many posts) but I am curious about how do you measure your firewall performance when testing fq_codel. Do you use a local testing environment? Additionally, have you tried to use just CoDel, PIE or Tail Drop with traffic shaping (limiter) and see how many pps can be achieved? That is important to see which part causes a reduction in performance.

tman222

Hi @rasool - thanks for getting back to me. After reading your response, I decided to start over once more and followed your steps - i.e. I created child queues but did not enable Codel this time. After doing some initial testing, I'm happy to report that performance was similar to what I had before, so indeed it seems that Codel on the child queues is just being ignored. The only thing that would speak against that is that I found myself increasing the queue size (from the default 50) when I originally had Codel enabled on the child queues, and this did improve performance.

I also had one other quick question for you: Why are the child queues necessary in the first place if fq_codel has its own set of queues? Put another way, why can't the Limiter be applied directly to the firewall rules instead of the child queues underneath the limiter?

Thanks again for all your help, I really appreciate it.

markn6262

@tman222 Thanks for posting your question. Was wondering the same but hadn't got around to asking.

Rasool

@tman222
Thank you for testing and confirming that. Enabling Codel for child queues and increasing queue size should not improve the performance of fq_codel as well, similar to pipe/limiter case beacuse fq_codel bypass dummynet queues.

@tman222 said in Playing with fq_codel in 2.4:

I also had one other quick question for you: Why are the child queues necessary in the first place if fq_codel has its own set of queues? Put another way, why can't the Limiter be applied directly to the firewall rules instead of the child queues underneath the limiter?

@tman222 and @markn6262

A simple answer is because of current pfSense WebUI you need to create "child" queues. You can use fq_codel with just limters if the WebUI configures the pipe to use the created schdulare. Here is an example of how to use fq_codel without creating a queue (I haven't test that though).

ipfw pipe 1 config bw 800Mb sched 1
ipfw sched 1 config pipe 1 type fq_codel target 5ms interval 100ms quantum 1514 limit 1024 flows 1024 ecn

Basically, just sched <sched number> should be added to pipe configuration.
Please note that creating a pipe will also create a queue internally because dummynet needs a flowset to interact with packets. There is no way to send packets directly to fq_codel schdeuler.