"Mitigate bufferbloat" reduces download bandwidth by half

#1

When I enabled the “mitigate bufferbloat” on firmware 8.0.0 beta 3 I saw no difference, but I kept it enabled anyway.

Since then, I’ve installed 8.0.0 RC1, but I don’t know if it’s related.

My main Internet connection has 200 Mbps of download bandwidth, but yesterday I noticed that I was only getting ~100 Mbps on DSL Reports test, and A+ on everything, all the time.

By disabling “mitigate bufferbloat” I instantlty got 200 Mbps again, but with A instead of A+.

Does “mitigate bufferbloat” really have that high impact on download bandwidth?

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Firmware 8.0.0 is now in RC1
#2

I’m seeing the same thing here: had zero problems on 8.0.0 beta 3 (and the bufferbloat fix seemed to be working for me, my bufferbloat was a C+ without it and an A+ with it.)

Since upgrading to RC1 this morning, my download bandwidth is halved.

Balance One with dual 300mbps cable modem WANs.

Update: I tried toggling the mitigate bufferbloat fix on and off, and it’s definitely the cause.

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#3

If the befferbloat implementation is anything like SQM in Linux, then it is very resource intensive.

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#4

I forgot to mention I’m using the Balance One too.

My connections are 200/100 and 15/8 (download/upload).

I believe I’m getting A on DSL Reports without the “mitigate bufferbloat” option because I’m using custom “WAN Connection Buffer Size”: 2100 and 170. I set those numbers so I have ~250ms of upload buffer.

Maybe the default size is ok for my current connection, but I used to have 15/2 and 10/0.6 connections. Back at that time, any upload would make my connections unusable before I set very low buffer sizes for both connections.

I’ll keep “mitigate bufferbloat” off until we get more information on how it works or until they fix any bug it might have. I understand this is experimental, so they may be trying new stuff between releases that are not documented.

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#5

Bump. Can we get a comment from peplink? Do you need a trouble ticket created? Thanks!

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#6

Hi All,
Thanks for your feedback. We have already taken note of this issue. 8.0.0 Beta 3 release provided bufferbloat mitigation only on “uplink” traffic which reduced latency during uploads. In 8.0.0 RC1, we added the support for “downlink” traffic as well. Even though it helps in better bufferbloat mitigation, it is causing a downlink performance drop which isn’t acceptable. Hence we have decided to rollback the downlink patch. 8.0.0 RC2 will have similar behaviour to Beta 3 for this feature.

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#7

I am experimenting with 8.0.0 RC3, #4178 on my Balance One. I haven’t used any of the prior 8.x beta releases. Where are the settings to manage bufferbloat? I’m trying this out on my home router before introducing 8.x in our company.

When I run the bufferbloat test at http://www.dslreports.com/speedtest, I got an F-rating with firmware 7.1, and the same with 8.0.0 RC3. Should I see some kind of improvement or do I have to turn on the feature somewhere?

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#8

I dont believe RC3 has been released yet…

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#9

Good catch, should be RC2 !! :smile:

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#10

It is a hidden feature.


@Don_Ferrario do you mind sharing your impression about the impact of the bufferbloat management?

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#11

OK I went to the hidden page and found the switch, thank you. Can’t say I have a full impression yet but the results are interesting. All below are using a Balance One, 8.0 RC2, and a Spectrum consumer grade cable internet with an advertised speed of 100m down and 10m up.

Running the tests with Peplink’s bufferbloat turned off, the results are the same as they were with firmware 7.1.1. Pretty bad bufferbloat:
downlink the curved graph continued to climb reaching over 2100ms. Speed 115-118M.
uplink the curve graph climbed to about 800ms. Speed 11M.

8.0.0 RC2 with mitigate bufferbloat enabled:
As expected no change to downlink. Per @shivanik above, that feature has no effect in RC2.
Uplink is greatly improved. The curved graph generally bounced around 10 to 25 ms, thats 1/10th of what it was doing before.
No change to upload or download speeds

I played with the Peplink experimental feature of reducing the buffer size. The default is 2,000 frames. I tried 200 and 20. Neither of those improved anything. In fact the uplink had more bufferbloat with the reduced buffer size. I speculate that manually changing the buffer size may defeat the mitigate bufferbloat option. I changed it back to the default.

Next I experimented with the Upload and Download bandwidth settings on the WAN settings page, with mitigate bufferbloat enabled. The thought above that reducing the setting made sense. Ultimately after a dozen tests I came to the conclusion that there was no effect on bufferbloat. Interestingly, there was also no effect on download/upload speed, even when I set the download speed to 50m (half the expected speed). It still stayed in the range of 115m down and 11m up.

Seeing as that last test accomplished nothing, I thought what the heck let’s try it the other way. I increased the WAN settings for upload and download. I realize that would totally screw up the load balancing but I only have one WAN at home. I don’t know why but doing this helped the downlink bufferfloat quite a bit. At 500-800ms its still a poor test result but its a whole lot better than 2100ms. The uplink was not affected by this, still reporting very little bufferbloat. Upload and download speeds were not affected in any of these tests.

Far from a conclusive test but clearly the mitigate bufferbloat feature basically eliminates the problem on uplink I don’t know why increasing the download speed setting helped so much but it is repeatable.

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#12
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