CoDel - How to use
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PFSense only implements the original Codel which has a large buffer length and has a target latency of 5ms. This allows it to do well if lots of small or large packets come through at the same time. One of the big issues with buffer bloat is if you buffer is too small you can drop small packets, but if your buffer is too large, then large packets cause too much back-log.
fq_Codel extends this to include "fair" queuing which breaks up data flows into hash buckets and does a mixture of prioritizing packets arriving into empty buckets and dequeing back-logged buckets equally. Codel is still pretty much the best option for now. Set and forget.
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Some have said CoDel is not a traffic shaper. This is confusing because CoDel drops packets to keep the buffers in check. Dropped TCP packets result in a throttling effect.
Perhaps I am confusing a "traffic shaper" with a "traffic policer".
http://www.cisco.com/c/en/us/support/docs/quality-of-service-qos/qos-policing/19645-policevsshape.htmlCoDel is one of the 2 though, right?
I am confused. :o
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To oversimplify it quite a bit:
Shaping can delay sending traffic (as well as drop) to smooth out usage, whereas policing simply lops off anything over the max rate and chucks it in the bit bucket.
Shaping typically employs queues as well as the occasional drop, whereas policing just says "nope" and drops it hard if it crosses the high rate.
Policing is very harsh, if you have ever had to deal with a circuit that had traffic policing, you know that both ends MUST have the same policing set or it's a nightmare of dropped packets. I haven't personally seen a circuit with traffic policing in probably 10 yrs or so, thankfully.
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Some have said CoDel is not a traffic shaper. This is confusing because CoDel drops packets to keep the buffers in check. Dropped TCP packets result in a throttling effect.
Perhaps I am confusing a "traffic shaper" with a "traffic policer".
http://www.cisco.com/c/en/us/support/docs/quality-of-service-qos/qos-policing/19645-policevsshape.htmlCoDel is one of the 2 though, right?
I am confused. :o
Traffics shapers do not drop packets, they dequeue packets queues at specified rates. It's the queue's drop packets, but the traffic shaper's job to decide which queue and when.
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Some have said CoDel is not a traffic shaper. This is confusing because CoDel drops packets to keep the buffers in check. Dropped TCP packets result in a throttling effect.
Perhaps I am confusing a "traffic shaper" with a "traffic policer".
http://www.cisco.com/c/en/us/support/docs/quality-of-service-qos/qos-policing/19645-policevsshape.htmlCoDel is one of the 2 though, right?
I am confused. :o
Traffics shapers do not drop packets, they dequeue packets queues at specified rates. It's the queue's drop packets, but the traffic shaper's job to decide which queue and when.
I think I understand what you are saying, but he post above you and the Cisco link both say that shapers drop packets. :o
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Shaping can drop but only by way of it dropping out of a queue. It still had to be queued, possibly delayed, etc.
The only action of Policing is to drop, no queue.
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Perhaps it is my confusion between incoming and outgoing egress. CoDel throttles (shapes?) incoming egress TCP streams based on queueing delay, but this queueing delay is controlled by outgoing egress speeds, which are controlled by the traffic-shaper.
I should probably just head back to the books… :-X
:D
Edit: I am referring to WAN interface.
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Codel is just a regular queue. Just like when the default queue gets full, it drops packets. The difference is the default queue does tail drops and does abrupt drops once full. Codel does head drops and defines full not as a number of packets but how long a packet was in the queue, even then, it doesn't do abrupt drops does does ever increasing rates of drops.
It is impossible to have a network interface without a queue, even if it's a queue of one. The whole point of a queue is to buffer packets. Codel does so in a way that reduces buffer bloat while allowing high throughput relative to the default fixed-size tail-drop that has been around for decades.
When writing multi-threaded code, you use queues a lot because synchronizing threads is expensive and you rarely have two threads that process data at the same rate. You need to buffer that data somewhere. Queues!
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I think I get it.
Part of my confusion stemmed from when I tested CoDel, it caused my upload/download to drop to ~75% of my maximum bitrate and the throughput was unsteady. I never experienced this problem with "regular" queues. This caused me to assume that CoDel was doing something extra (shaping) to keep my queueuing delay low. Without CoDel, I achieved the bitrate assigned to the interface.
I now realize that CoDel should not have acted that way. I will need to revisit CoDel and see if I get the same results again.
My real-world internet speeds are 6.34Mb/666Kb.
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I think I get it.
Part of my confusion stemmed from when I tested CoDel, it caused my upload/download to drop to ~75% of my maximum bitrate and the throughput was unsteady. I never experienced this problem with "regular" queues. This caused me to assume that CoDel was doing something extra (shaping) to keep my queueuing delay low. Without CoDel, I achieved the bitrate assigned to the interface.
I now realize that CoDel should not have acted that way. I will need to revisit CoDel and see if I get the same results again.
My real-world internet speeds are 6.34Mb/666Kb.
Did you set an upload bandwidth limit? Set it at 95% if 666Kb and have another run at it.
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I think I get it.
Part of my confusion stemmed from when I tested CoDel, it caused my upload/download to drop to ~75% of my maximum bitrate and the throughput was unsteady. I never experienced this problem with "regular" queues. This caused me to assume that CoDel was doing something extra (shaping) to keep my queueuing delay low. Without CoDel, I achieved the bitrate assigned to the interface.
I now realize that CoDel should not have acted that way. I will need to revisit CoDel and see if I get the same results again.
My real-world internet speeds are 6.34Mb/666Kb.
Did you set an upload bandwidth limit? Set it at 95% if 666Kb and have another run at it.
I did. I usually set to less than 600Kbit. CoDel's official site states that <768Kbit connections are troublesome.
Though, the reason for my download falling from ~730kB/sec without CoDel to ~500kB/sec with CoDel is still unknown to me. I had this type of result numerous times.
I may have misconfigured something back when I tested. Hopefully that explains it… :)
I used the CODELQ setup, not the "Codel Active Queue" check-box.
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Codel uses a target of 5ms, which at 768Kb/s is only 480bytes. This means a single 1500byte packet will cause Codel to want to start dropping packets. On my 100Mb connection, 5ms is 62,500 bytes, which is nearly 42 1500 byte packets. A single 1500 byte packet is 5ms at 2.4Mb/s. May be best to recommend Codel to be only implemented on 3Mb/s+ connections. fq_Codel probably wouldn't fair much better for bandwidth utilization, but would do better for not dropping small packets that immediately followed a 1500byte packet.
I think I remember reading that 10Mb+ is recommended for Codel, but I'm not sure if that was an official value or just an easy to remember number given as a rule of thumb.
Anyway, 1500 bytes is way to large for slow connections when latency is an issue.
edit: I think the 10Mb comment was in reference that 5ms is not optimal for connections below 10Mb, but not to say it won't work. I assume there is a lower bound where Codel is definitely not good, like the 657Kb someone else said they read or the 2.4Mb/s rate required to transmit 1500 bytes in 5ms.
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I just tried the "Codel Active Queue" on my outgoing bulk HFSC queue and it worked like a charm. Dropped my average queue size from ~30 to ~1 and dropped my ping from ~600ms to ~50ms during a single stream upload.
Now I need to test out FAIRQ with Codel check-marked to see how that setup deals with multiple concurrent streams.
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Hmm… I just ran into an unexpected negative side-effect of CoDel. I knew it had some drawbacks. ;)
I check-marked Codel on my WAN HFSC qBulk queue, that was configured to have an increased worst-case delay with link-share [0Kb, 25, 300Kb], so other packets would be prioritized. It also had a queue limit of 500, so that if things got bad, it could just queue up packets and let the delay climb, but. CoDel won't allow that, because it keeps the packet queueing delay at 5ms… right?
Without much consideration, I excitedly chose to decrease the delay of the my greediest queue to resultingly decrease the delay of all other queues. Dumb... I think I should have taken the more direct route of exclusively decreasing the delay of the non-qBulk queues, leaving qBulk to become backlogged and delayed as it increasingly yields to packets with more priority.
Small queues are not always the answer, apparently. :)
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I have a 15m/1m DSL line and tried implementing CoDel in pfSense last night. I was not able to detect any improvement, so I deleted the discipline; which in turn crashed pfSense and I had to reboot, which made me wonder if I did things right or not.
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I have a 15m/1m DSL line and tried implementing CoDel in pfSense last night. I was not able to detect any improvement, so I deleted the discipline; which in turn crashed pfSense and I had to reboot, which made me wonder if I did things right or not.
No, lol… I experience the same thing; Put a traffic-shaper queue on LAN, remove it... crash. Though, pfSense did unfreeze itself once, but it took a good 60+ seconds
About your poor experience; CoDel or not, you should see latency improvement if you configured your pfSense gateway as the slowest hop in your route. Transferring egress queueing from your modem to pfSense and your ingress queueing from your ISP to pfSense, should always see some sort of improvement, unless you are lucky enough to have a great ISP.
What were you results exactly?
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Nullify wrote:
"About your poor experience; CoDel or not, you should see latency improvement if you configured your pfSense gateway as the slowest hop in your route. Transferring egress queueing from your modem to pfSense and your ingress queueing from your ISP to pfSense, should always see some sort of improvement, unless you are lucky enough to have a great ISP."
Could you please describe how to do that "for the complete idiot?"Â Thanks.
I tested the changes with the new speed test over at DSL Reports (which has a buffer bloat meter–don't know exactly how it works).
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Just make sure that your pfSense router is the slowest part of your upload and download traffic.
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I love that new speed test. Should I have not been seeding 30Mb/s while running this test? lololol
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Nullify wrote:
"Just make sure that your pfSense router is the slowest part of your upload and download traffic."
So, in order to do that, should I use the traffic shaping wizard (where CoDel is not an option) to set my bandwidth (and leave all other settings on default, since I don't need to prioritize traffic), or should I use the CODELQ option under "By Interface?"
Someone really should write the book, pfSense for Dummies.
