[Bloat] Win10 Updates vs cake

Ryan Mounce ryan at mounce.com.au
Thu Dec 21 21:55:03 EST 2017

I've experienced this recently myself. In my case I have a 100Mbps
link from my ISP and their shaper will queue up to about 120ms worth
of packets (on top of the ~10ms baseline latency). I run cake in
ingress mode at 99.2Mbps, which has normally been enough to keep
everything in check and keep my ISP's queue empty at least in the
steady state.

Boot up a Windows 10 PC that's been unused for a few months, let it
update and bam! 100-130ms RTT, family member's Netflix stream in the
next room stalls completely, and running a quick speedtest on a
different machine (that should get ~50% share of the link under normal
circumstances with dual-dsthost) yields about 1.2Mbps on a 100Mbps
link! I performed a quick pcap while this was happening and determined
that Windows Update had started on the order of 120 parallel HTTP
downloads from 2 different Akamai cache IPs (within my ISP's network
20ms away).

The 20ms jump in latency in your case just indicates that there is a
small buffer in your DSLAM, however it is still being flooded by the
parallel transfers from the CDN.

Windows 10 probably deserves most of the blame for opening so many
parallel connections, however I think there is also some concern here
with Akamai's FastTCP not responding to congestion signals.

Ryan Mounce

On 22 December 2017 at 12:31, Rich Brown <richb.hanover at gmail.com> wrote:
> I'm using LEDE 17.01.4 on my Archer C7v2. I have a 7mbps/768kbps ADSL2+ connection through Fairpoint. The modem stats page shows its "attainable rates" (kbps): 13330/1272 and Rates: 8271/1181. My SQM settings are:
> Download: 7000 (kbps)
> Upload: 925
> Queue Disc: Cake/piece_of_cake.qos
> Link Layer: ATM/44 bytes overhead
> Advanced Options: default
> I have noticed that Win10 updates cause the network connection to become unusable for other services/people, as if I had bufferbloat. But ping times remain stable - they jump from ~20-22 msec unloaded to 40-50 msec.
> Experiments I have tried:
> - Setting download speed to 5000 makes the connection usable for other people, although the ping times remain about the same (40-50 msec)
> - Setting the download speed to 8600 still keeps ping times down, but that really harms other people's performance.
> - The link rates (download and upload) seem to track the SQM setting, measured with both YAMon and the built-in real-time graphs.  I get ~6,000 kbps with a 7000 download setting, I got ~3,000kbps at the 5000 setting. I get ~8500 kbps after setting download to 8600.
> - This doesn't seem to happen when I'm downloading other kinds of files (I haven't tried torrenting files...) Downloading non-Win10 update files seems to leave the connection in a fairly responsive state.
> Any thoughts? What other experiments should I make? Thanks!
> Rich
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