CoDel - How to use



  • @tuffcalc:

    I take back what I said about Codel.  When I saturate the upload fully for a long period of time my pings still shoot through the roof (200+ ms).

    Try settings your WAN rate to about 95% of your stable upload rate and see what happens.



  • @Harvy66:

    @tuffcalc:

    I take back what I said about Codel.  When I saturate the upload fully for a long period of time my pings still shoot through the roof (200+ ms).

    Try settings your WAN rate to about 95% of your stable upload rate and see what happens.

    That fixed it…



  • @tuffcalc:

    @Harvy66:

    @tuffcalc:

    I take back what I said about Codel.  When I saturate the upload fully for a long period of time my pings still shoot through the roof (200+ ms).

    Try settings your WAN rate to about 95% of your stable upload rate and see what happens.

    That fixed it…

    Well, 200ms is a lot less than what I thought it would have been, so just enabling CoDel without setting bandwidth is probably doing something, just not as effective as in conjunction with settings your bandwidth.

    Just wondering, what was your ping during saturation when you have your bandwidth set?



  • @Harvy66:

    @tuffcalc:

    @Harvy66:

    @tuffcalc:

    I take back what I said about Codel.  When I saturate the upload fully for a long period of time my pings still shoot through the roof (200+ ms).

    Try settings your WAN rate to about 95% of your stable upload rate and see what happens.

    That fixed it…

    Well, 200ms is a lot less than what I thought it would have been, so just enabling CoDel without setting bandwidth is probably doing something, just not as effective as in conjunction with settings your bandwidth.

    Just wondering, what was your ping during saturation when you have your bandwidth set?

    I've been all over the place and probably gave some false information (because I am new to this and didn't really understand what I was doing).  Anyway, let me try and clear up my findings:

    1. No traffic shaping, all bandwidth available - ping 10ms
    2. No traffic shaping, download saturated - ping 60ms
    3. No traffic shaping, upload saturated - ping 500+ms

    4. CODEL active with no bandwidth limit set - all pings same as scenarios 1,2 & 3.

    5. CODEL active (WAN side only) with bandwidth limit set at 98% of uplink speed, all bandwidth available - ping 10ms
    6. CODEL active (WAN side only) with bandwidth limit set at 98% of uplink speed, download saturated - ping 60ms
    7. CODEL active (WAN side only) with bandwidth limit set at 98% of uplink speed, upload saturated - ping 50 to 80ms

    So it does work, although during a saturated upload I notice my VoIP phone going a bit "robotic", but much improved over no traffic shaping (VoIP calls would be largely unusable).  Did not have that issue with PRIQ when prioritizing VoIP as first in line.  That being said, CODEL is much easier to setup and it looks like it doesn't completely starve other queues like PRIQ.  I'm sticking with CODEL.

    Interested to see if FQ_CODEL will make my pings even lower.  Will test it as soon as it is available in pfsense.



  • @tuffcalc

    Thanks for the info. I've done my fair share of "false" information with good intentions. It happens.

    Yes, the whole PRIQ replacement is kind of interesting. The eventual fq_codel will actually do similar things of PRIQ, but better for general usage. Except in the case where you need certain traffic to always get priority, fq_codel will do what most people want, keep latency low without the hassle of floating rules.


  • Rebel Alliance Developer Netgate

    @tuffcalc:

    @Harvy66:

    @tuffcalc:

    @Harvy66:

    @tuffcalc:

    I take back what I said about Codel.  When I saturate the upload fully for a long period of time my pings still shoot through the roof (200+ ms).

    Try settings your WAN rate to about 95% of your stable upload rate and see what happens.

    That fixed it…

    Well, 200ms is a lot less than what I thought it would have been, so just enabling CoDel without setting bandwidth is probably doing something, just not as effective as in conjunction with settings your bandwidth.

    Just wondering, what was your ping during saturation when you have your bandwidth set?

    I've been all over the place and probably gave some false information (because I am new to this and didn't really understand what I was doing).  Anyway, let me try and clear up my findings:

    1. No traffic shaping, all bandwidth available - ping 10ms
    2. No traffic shaping, download saturated - ping 60ms
    3. No traffic shaping, upload saturated - ping 500+ms

    4. CODEL active with no bandwidth limit set - all pings same as scenarios 1,2 & 3.

    5. CODEL active (WAN side only) with bandwidth limit set at 98% of uplink speed, all bandwidth available - ping 10ms
    6. CODEL active (WAN side only) with bandwidth limit set at 98% of uplink speed, download saturated - ping 60ms
    7. CODEL active (WAN side only) with bandwidth limit set at 98% of uplink speed, upload saturated - ping 50 to 80ms

    So it does work, although during a saturated upload I notice my VoIP phone going a bit "robotic", but much improved over no traffic shaping (VoIP calls would be largely unusable).  Did not have that issue with PRIQ when prioritizing VoIP as first in line.  That being said, CODEL is much easier to setup and it looks like it doesn't completely starve other queues like PRIQ.  I'm sticking with CODEL.

    Interested to see if FQ_CODEL will make my pings even lower.  Will test it as soon as it is available in pfsense.

    Out of curiosity, which exact places do you have CoDel active for? As the shaper discipline for the interface, or using HFSC with "Codel Active Queue" on specific queues? And if the latter, which queues?

    The more good/working examples we can get the better, I can put them up on the wiki for future reference.



  • @jimp:

    @tuffcalc:

    @Harvy66:

    @tuffcalc:

    @Harvy66:

    @tuffcalc:

    I take back what I said about Codel.  When I saturate the upload fully for a long period of time my pings still shoot through the roof (200+ ms).

    Try settings your WAN rate to about 95% of your stable upload rate and see what happens.

    That fixed it…

    Well, 200ms is a lot less than what I thought it would have been, so just enabling CoDel without setting bandwidth is probably doing something, just not as effective as in conjunction with settings your bandwidth.

    Just wondering, what was your ping during saturation when you have your bandwidth set?

    I've been all over the place and probably gave some false information (because I am new to this and didn't really understand what I was doing).  Anyway, let me try and clear up my findings:

    1. No traffic shaping, all bandwidth available - ping 10ms
    2. No traffic shaping, download saturated - ping 60ms
    3. No traffic shaping, upload saturated - ping 500+ms

    4. CODEL active with no bandwidth limit set - all pings same as scenarios 1,2 & 3.

    5. CODEL active (WAN side only) with bandwidth limit set at 98% of uplink speed, all bandwidth available - ping 10ms
    6. CODEL active (WAN side only) with bandwidth limit set at 98% of uplink speed, download saturated - ping 60ms
    7. CODEL active (WAN side only) with bandwidth limit set at 98% of uplink speed, upload saturated - ping 50 to 80ms

    So it does work, although during a saturated upload I notice my VoIP phone going a bit "robotic", but much improved over no traffic shaping (VoIP calls would be largely unusable).  Did not have that issue with PRIQ when prioritizing VoIP as first in line.  That being said, CODEL is much easier to setup and it looks like it doesn't completely starve other queues like PRIQ.  I'm sticking with CODEL.

    Interested to see if FQ_CODEL will make my pings even lower.  Will test it as soon as it is available in pfsense.

    Out of curiosity, which exact places do you have CoDel active for? As the shaper discipline for the interface, or using HFSC with "Codel Active Queue" on specific queues? And if the latter, which queues?

    The more good/working examples we can get the better, I can put them up on the wiki for future reference.

    It's active only for the shaper discipline for the WAN interface.


  • LAYER 8 Netgate

    It's active only for the shaper discipline for the WAN interface.

    OK.  Now I'm confused.  If codel has no knobs, what is actually doing the shaping based on the bandwidth value?



  • @Derelict:

    It's active only for the shaper discipline for the WAN interface.

    OK.  Now I'm confused.  If codel has no knobs, what is actually doing the shaping based on the bandwidth value?

    CoDel is not a traffic shaper, it does not do any rate limiting, that is the job of your rate limiter. All CoDel does is figure out which packets to dequeue next or which to drop.

    See my quotes from the makers of CoDel

    https://forum.pfsense.org/index.php?topic=88162.msg488220#msg488220


  • LAYER 8 Netgate

    Exactly.

    The question I have is why tuffcalc sees a difference in behavior when he sets a bandwidth value of 98% of his upload when his scheduler type is CODELQ?

    As I understand codel, it should make no difference, so what is actually doing the shaping?  Is it built into altq itself absent any HFSC, PRIQ, etc?



  • Ahh.. I assumed PFSense/FreeBSD had a built in interface rate limiter that functioned separately of queue management like AQMs or shapers. To me, they are all orthogonal problems. The interface can be rate limited and not care about how queues are implemented, how many queues there are, or which queue to dequeue next. Traffic shapers can decide which queues to pull from and how fast to dequeue those queues, and AQMs can decide which packet to dequeue from a given queue.

    Interface->InterfaceRateLimiter->TrafficShaper(HFSC)->AQM(CoDel)

    Like a pipeline, with none needing to know anything about the others. Not to say this is how it is implemented, but it could be implemented this way as none of them have any overlap or unique dependencies on each other. Some traffic shapers may need to know how fast to expect the interface to dequeue from them.  HFSC might not actually be really "limiting", it might be just "scheduling", while the interface limiter might be doing the limiting. I'm not sure about implementation details, just looking at it from an abstract point of view and what could be done. I am ignoring the fact that HFSC does have the notion of an upper bound, but ignoring that, pretty much all other features of HFSC could be done without any rate limiting, only scheduling.


  • LAYER 8 Netgate

    This is what I get when I set scheduler type to CODELQ and a 900Mbit bandwidth:

    altq on  em0_vlan1003 codelq bandwidth 900Mb queue

    Absent any other requirements, that is probably sufficient to eliminate any buffer bloat one might have at their ISP (assuming bandwidth set to about 90-95% of reasonably-expected uplink.)



  • This is a very informative thread, I've been searching this forum on general traffic shaping methods / tricks and I've bookmarked a couple of threads including this one…I'm yet do to my setup, I like doing the research first so I can have an idea of what I'm dealing with.

    I have a question tho'; from what I read CoDel is only meant to work (well) with high speed connections? 2.5mbit and above?. I'm currently using a very low ADSL connection 1770kbps down 550kbps up (thats what I get from speedtest although the ISP sells as 2mbit down 1mbit up), would CoDel work for me with this speeds?

    I'm looking to upgrade to 10mbit down 2.5mbit up soon but I kindly need to know if CoDel would work for me with my current speeds.

    Another question is; I'm I right to assume that CoDel can work side to side with PRIQ and the Limiter (I intend to use the Limiter to implement share bandwidth evenly on LAN as foxale08 has illustrated here; https://forum.pfsense.org/index.php?topic=63531.0 )

    Regards.



  • @cmutwiwa:

    This is a very informative thread, I've been searching this forum on general traffic shaping methods / tricks and I've bookmarked a couple of threads including this one…I'm yet do to my setup, I like doing the research first so I can have an idea of what I'm dealing with.

    I have a question tho'; from what I read CoDel is only meant to work (well) with high speed connections? 2.5mbit and above?. I'm currently using a very low ADSL connection 1770kbps down 550kbps up (thats what I get from speedtest although the ISP sells as 2mbit down 1mbit up), would CoDel work for me with this speeds?

    I'm looking to upgrade to 10mbit down 2.5mbit up soon but I kindly need to know if CoDel would work for me with my current speeds.

    Another question is; I'm I right to assume that CoDel can work side to side with PRIQ and the Limiter (I intend to use the Limiter to implement share bandwidth evenly on LAN as foxale08 has illustrated here; https://forum.pfsense.org/index.php?topic=63531.0 )

    Regards.

    Answer to your first question: No (but it couldn't hurt to try… :))

    If you check CoDel's official site you would see that there are a few known problems. Here is a quote from  http://www.bufferbloat.net/projects/codel/wiki/Wiki/

    At very low bandwidths (e.g. .5Mbps) on ADSL, we're having to play with the target; Kathie did not have to in her simulations. This is due to inevitable buffering
    in htb or in the device driver. We have a version under development that does bandwidth limiting without buffering an extra packet, called cake. It's looking good so far.

    The quote mentions "playing with the target", but this level of configuration is only available in the Linux kernel's Codel/fq_codel implementation (please correct me if I am wrong). I am assuming they mean target delay. Please refer to to the following link for more information:  http://man7.org/linux/man-pages/man8/tc-fq_codel.8.html

    Regarding your second question; I have only used Codel as a stand-alone queue, never as part of another queueing algorithm like PRIQ or HFSC. I have no reason to think it wouldn't work though. Make sure to reset the firewall states and test your queueing configuration to confirm that it is working as expected.



  • I use Codel in conjunction with HFSC on my 100/100 connection. In theory they're independent of each other. HFSC schedules which queue to dequeue and Codel deiced which packets to dequeue or to drop.

    In practice, I never see any packets dropped according to the queue statistics, but I also never see any measurable latency spikes.

    I'm not sure of a goad way to load test because my connection is "too" stable.

    It is possible that if HFSC isn't "smooth" enough at interleaving the queues, a queue could wait longer than what Codel wants and could create packetloss when there isn't any real congestion, but HFSC seems like freaking magic. I assume bad things could happen with an older machine with 10ms timers or 10/40Gb interfaces that have fq_Codel tuned for 0.5ms, which is recommended for those rates. but right now, we do not have fq_codel nor do we have a way to tweak the target delay via the interface.



  • Here is how I have mine setup for testing right now:
















  • @Nullity:

    Answer to your first question: No (but it couldn't hurt to try… :))

    If you check CoDel's official site you would see that there are a few known problems. Here is a quote from  http://www.bufferbloat.net/projects/codel/wiki/Wiki/

    Thanks, will give it a try.

    I'm hoping it will work smoothly with PRIQ and the Limiter, I would achieve alot!



  • I have been experimenting with my home router which is running DD-WRT and enabled HTB along with FQ_CoDel. My latency under load has improved from 300ms+ to just under 20ms+ as measured by pinging Google DNS. The connection is a Frontier FIOS 25M/25M. My throughput as verified by speedtest.net are good whether I am using a Seattle based server or one in Atlanta. I thought that was great and looked into turning CoDel on in pfSense at work.

    We have two pfSense firewalls both in the Seattle area. One is sitting on a 50M/50M Comcast EDI circuit. The other one is sitting on a collocated burstable gigabit circuit that we shape to 100M/100M. Both use a simple PRIQ shaper with 500 packet queue limit, that's roughly a max queue delay of 114ms for 50M and 57ms for 100M. I have found that the 500 packet queue limit offers the best throughput performance with least drops and this has worked for us for a few years now.

    For most general traffic I really don't care that it queues up and gets delayed, but less intensive flows should not get delayed. Which I see CoDel doing on my home router. pfSsense was able to do the same on our work connections. However, something weird is going on when I do speed tests from the pfSense boxes. When I choose a local Seattle server with an RTT of under 10ms, both connections approach close to their shaped throughput. When I choose a server in Atlanta or Miami where the RTT is around 80ms, suddenly the upload throughput is 25-50% less, and it takes longer to get up to that throughput. Download throughput is never affected even though CoDel is enabled on the LAN queues and I verified that it is working via ping. If I turn off CoDel AQM, the upload for high RTT servers goes back to roughly shaped throughput.

    Can anyone explain why the longer RTT is causing issues for upload on pfSsense using CoDel. Why does DD-WRT not experience this issue?



  • Are you using the same computer when doing speed tests? I've seen large variations in speed tests between computers. Too bad PFSense doesn't have fq_codel yet, but there are some other awesome changes in the pipeline.



  • @Harvy66:

    Are you using the same computer when doing speed tests? I've seen large variations in speed tests between computers. Too bad PFSense doesn't have fq_codel yet, but there are some other awesome changes in the pipeline.

    I am using Windows Server 2008 R2 when testing the work connections. I am using Mac OS X 10.10.2 and Windows 8.1 Pro at home. I'll see if Windows 8.1 Pro makes a difference on the office connection tomorrow, though I doubt it.

    I am thinking that the queue length has something to do with it on pfSense.



  • @ltctech:

    @Harvy66:

    Are you using the same computer when doing speed tests? I've seen large variations in speed tests between computers. Too bad PFSense doesn't have fq_codel yet, but there are some other awesome changes in the pipeline.

    I am using Windows Server 2008 R2 when testing the work connections. I am using Mac OS X 10.10.2 and Windows 8.1 Pro at home. I'll see if Windows 8.1 Pro makes a difference on the office connection tomorrow, though I doubt it.

    I am thinking that the queue length has something to do with it on pfSense.

    If stream fairness is your goal then FAIRQ might be a better choice. There is a picture somewhere showing graphs of fq_codel, codel, SFQ (stochastic fair queue) and the latency changes when each algorithm is dealing with dozens of simultaneous streams. SFQ was a close 2nd behind fq_codel for best latency. FAIRQ is very similar to SFQ (both give each stream a hash then iterate through them round-robin style).

    Codel is lacking "fair queueing" (there are many papers on this topic) so it does poorly with multiple streams, unlike fq_codel.



  • @ltctech:

    @Harvy66:

    Are you using the same computer when doing speed tests? I've seen large variations in speed tests between computers. Too bad PFSense doesn't have fq_codel yet, but there are some other awesome changes in the pipeline.

    I am using Windows Server 2008 R2 when testing the work connections. I am using Mac OS X 10.10.2 and Windows 8.1 Pro at home. I'll see if Windows 8.1 Pro makes a difference on the office connection tomorrow, though I doubt it.

    I am thinking that the queue length has something to do with it on pfSense.

    There are a few things at play.

    1. If your queue is too small, it will drop packets too aggressively. You can look at queue statistics to find out if there are any drops happening.
    2. If your queue is too large and are not using something like Codel with time based dropping, your bandwidth can also be made less efficient
    3. My personal most common reason for poor upload speeds is the TCP stack of the OS I'm using

    Windows 202 R2 is the Win7 kernel, and Win7 defaults to some latency sensitive TCP congestion control. This may not be the same for the server edition, but when I switched to using CTCP, my upload bandwidth to higher latency targets increased substantially. Win8 of all versions default to CTCP.

    And never assume two similar machines would get the same performance. I had two identical computers, exactly the same hardware, both with a fresh install of Win7, and one was over 50% faster than the other for speed tests. The only thing I could think of that would make the difference was heuristics. Win7 tries to be "smart" about certain things, which can cause it to get confused. A quick trip into the registry to change some settings and a reboot and both systems were getting identical speedtests.

    So even freshly installed identical hardware can get large variations. ALWAYS test using the same machine. Or use an OS that doesn't suck. Freaking Windows.



  • @Harvy66:

    @ltctech:

    @Harvy66:

    Are you using the same computer when doing speed tests? I've seen large variations in speed tests between computers. Too bad PFSense doesn't have fq_codel yet, but there are some other awesome changes in the pipeline.

    I am using Windows Server 2008 R2 when testing the work connections. I am using Mac OS X 10.10.2 and Windows 8.1 Pro at home. I'll see if Windows 8.1 Pro makes a difference on the office connection tomorrow, though I doubt it.

    I am thinking that the queue length has something to do with it on pfSense.

    There are a few things at play.

    1. If your queue is too small, it will drop packets too aggressively. You can look at queue statistics to find out if there are any drops happening.
    2. If your queue is too large and are not using something like Codel with time based dropping, your bandwidth can also be made less efficient
    3. My personal most common reason for poor upload speeds is the TCP stack of the OS I'm using

    Windows 202 R2 is the Win7 kernel, and Win7 defaults to some latency sensitive TCP congestion control. This may not be the same for the server edition, but when I switched to using CTCP, my upload bandwidth to higher latency targets increased substantially. Win8 of all versions default to CTCP.

    And never assume two similar machines would get the same performance. I had two identical computers, exactly the same hardware, both with a fresh install of Win7, and one was over 50% faster than the other for speed tests. The only thing I could think of that would make the difference was heuristics. Win7 tries to be "smart" about certain things, which can cause it to get confused. A quick trip into the registry to change some settings and a reboot and both systems were getting identical speedtests.

    So even freshly installed identical hardware can get large variations. ALWAYS test using the same machine. Or use an OS that doesn't suck. Freaking Windows.

    You are right about the TCP stack differences. Windows 2008 R2 copes much worse than Windows 8.1 or Windows 2012 R2. Though even in Windows 8.1 where I checked that CTCP is enabled, I am getting an average upload of 40-45Mbits where it should be 48-49Mbits. So I guess CoDel is just not worth it, at least how its implemented on pfSense. Maybe they'll fix it when they do FQ_CoDel.



  • 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.



  • 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.html

    CoDel is one of the 2 though, right?

    I am confused. :o


  • Rebel Alliance Developer Netgate

    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.



  • @Nullity:

    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.html

    CoDel 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.



  • @Harvy66:

    @Nullity:

    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.html

    CoDel 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


  • Rebel Alliance Developer Netgate

    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.



  • 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.



  • 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!



  • 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.



  • @Nullity:

    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.



  • @tuffcalc:

    @Nullity:

    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.



  • 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.



  • 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.



  • 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. :)



  • 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.



  • @Nonsense:

    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?



  • 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?"  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).


Log in to reply