[Bloat] powerboost and sqm

[Sebastian Moeller]

Hi Jonas,

nice data.

> On Jun 29, 2018, at 12:56, Jonas Mårtensson <martensson.jonas at gmail.com> wrote:
> 
> Hi,
> 
> I have a 100/100 Mbit/s (advertised speed) connection over fiber (p2p, not PON). The actual link rate is 1 Gbit/s. My ISP seems to be using burst-tolerant shaping (similar to powerboost) as can be seen in this speedtest where the download rate is 300+ Mbit/s and the upload rate is around 150 Mbit/s for the first few seconds:
> 
> http://www.dslreports.com/speedtest/35205027
> 
> It can be discussed why they are doing this but my questions are more related to the impact on the quality of my connection. The ISPs shaper used to introduce some bufferbloat, especially on the downlink, and I've been using sqm for a while to mitigate this. But recently they seem to have changed some configuration since the bufferbloat is now almost zero, except for some very short spikes which only show up when I check "Hi-Res BufferBloat" in test preferences (see speedtest above). When I enable sqm on my router with htb/fq_codel or cake the spikes disappear:
> 
> htb/fq_codel:
> http://www.dslreports.com/speedtest/35205620
> 
> cake:
> http://www.dslreports.com/speedtest/35205718
> 
> Another difference is that the "Re-xmit" percentage (which I guess is related to packet loss) is much higher without sqm enabled. Intuitively this makes sense since temporarily allowing a higher rate should result in more buffer overflow when the rate is decreased.
> 
> So, what do you think:
> 
> - Are the latency spikes real?

	I believe so, but I would try to use flent's rrul test to see whether theses also show up outside of a browser-based test.


> The fact that they disappear with sqm suggests so but what could cause such short spikes? Is it related to the powerboost?

	I do not think so, as you have these spikes all over the upload test while the boost only last for around a third of the test.

> 
> - Would you enable sqm on this connection?

	Personally I would, but for me the per host isolation is one of the features I really like to have. 

> By doing so I miss out on the higher rate for the first few seconds. What are the actual downsides of not enabling sqm in this case?

	Well, you loose some bandwidth but that seems to be it, you gain all the other nice features that especially cake offers.

Best Regards
	Sebastian

> 
> /Jonas
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