[Bloat] Fwd: Did *bufferbloat* cause the 2010 flashcrash?

Steinar H. Gunderson sgunderson at bigfoot.com
Fri Aug 7 10:47:41 EDT 2015

On Fri, Aug 07, 2015 at 04:39:16PM +0200, Toke Høiland-Jørgensen wrote:
> 2. Bandwidth sharing between bittorrent and other protocols. Bittorrent
>    uses utp to try to be a scavenger that will back off and not use
>    bandwidth if other traffic needs it. fq_codel breaks this by
>    isolating flows and taking away the signal utp uses to back off.
>    Diffserv with a suitable scheduler (cake, for instance) can fix this
>    if the bittorrent client is configured correctly;

Well, I already pointed out that DSCP doesn't really work :-) For one, the
torrent client _isn't_ configured correctly. I have yet to actually see any
setting DSCP bits in practice, although I'm sure they exist (e.g. I heard
Dave was sending out patches).

>    or you could use
>    deep(er) packet inspection to try to figure out which traffic is
>    bittorent. But we don't have a shrinkwrap solution to this presently,
>    AFAIK.
> I believe the cat video upload falls into category 2.

Yes, certainly.

In a sense, the only reasonable solution I can see to this problem is to have
two-level fq_codel (fair between senders, fair between flows for each
sender), but that simply doesn't exist. Also you'd need to reverse it for
downloads, and for someone in the middle, who knows what's actually up or

/* Steinar */
Homepage: http://www.sesse.net/

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