[Cake] Getting Cake to work better with Steam and similar applications

xnoreq xnoreq at gmail.com
Sat Apr 22 08:50:25 EDT 2017

FYI, when I looked at Steam traffic a few years ago it was very bursty,
meaning that there is nothing transmitted for a short period and then
there's a burst that uses up all link bandwidth for a short while.
Internet was unusable without limiting Steam downloads quite a lot.

Now I don't have that problem anymore. Cake's ingress mode works almost as
well as I have expected (still need to set bw about 1Mbps lower on a 20Mbps
link - but that's ok).
Maybe the Steam CDN now also uses a saner network scheduler (like fq with
pacing). I'd guess so anyway.

On 22 Apr 2017 11:36, "Jonathan Morton" <chromatix99 at gmail.com> wrote:

> >> So please add “atm overhead 32" to cake on eth0 or “atm overhead 40” to
> cake instances on pppoe (these packets do not have the PPPoE header added
> yet and hence appear 8 bytes to small).
> >
> > Thanks for your help, will definitely use them. Just wondering if I use
> "pppoe-vcmux/bridged-llcsnap" on eth0 or "pppoe-llcsnap" on pppoe0 would
> have the same effect? Or are there some other "under-the-hood" changes when
> using them?
> On the pppoe interface, use pppoe-vcmux if your modem is set to use
> VC-MUX, or pppoe-llcsnap if it’s set to use LLC-SNAP (they might be
> described using slightly different terms, but should still be recognisable
> as one or the other).  This probably depends on your ISP, and may further
> vary regionally within the same ISP.
> I really prefer to use the self-explanatory keywords (which is why I added
> them in the first place) instead of opaque magic numbers.  This is a point
> on which Sebastian has long disagreed with me.
> >> Question: if you set the shaper’s to 50% of line rate (8.75/0.5?) do
> you still see that unfairness? And if you add “atm overhead 40” to cake on
> pppoe0 and set the shaper to 90% of line rates (15.75/0.9) how does the
> Steam affect per-host fairness? Also how transient are these connections
> team uses?
> >
> > Actually did more testing about this and it seems that as far I have set
> the bandwidth to ~15Mbps (so ~15% less of my max speed) and use the "nat"
> parameter, the per-host fairness works even without the "dual-host" and
> "overhead" parameters. I definitely find this very interesting, is this
> behaviour caused by the way Steam downloads games?
> By default, Cake uses triple-isolate mode, which uses information about
> both source and destination hosts to perform per-host isolation; this
> usually works well regardless of which side of the connection has the LAN
> hosts.  The “dual” modes let you specify that fact explicitly, making it a
> little more robust and predictable.
> Without overhead compensation, Cake will actually use more of the physical
> link than it thinks it does - by default it only accounts for raw IP or
> Ethernet packets, depending on the type of interface it’s attached to.
> With full-size packets as in a bulk download, the difference is relatively
> small, so the 15% margin is just about sufficient to make things work.  But
> with small packets mixed in, the difference grows, such that Cake might no
> longer control the bottleneck with some traffic mixes.
> The “conservative” keyword I recommended earlier (which is exactly
> equivalent to Sebastian’s recommendation of “atm overhead 48”) reverses
> that situation; Cake will then always end up using *less* of the physical
> link than it accounts for, which is safe for troubleshooting with.  The
> keyword is there specifically so that we do’t have to figure out the
> precise overhead profile before tackling more substantive issues.
> At any rate, it has nothing to do with Steam specifically.
> >> As far as I can tell cake can drill down to the required IP/TCP/UDP
> fields independent of whether there are VLAN tags or PPPoE headers so cake
> should not care (except for the different overhead specifications you need
> to add as stated above). BUT if instantiated on eth0 cake will see pppoe
> LCP packets and might decide to drop them, which can take down the link, so
> out of caution I would still instantiate on pppoe in your case.
> >
> > Yeah, with further testing it seems the interface wasn't the culprit but
> I'll still do all my testing on pppoe0 just to be safe.
> >
> > Anyway I was wondering if there's some kind of manual for Cake and the
> various parameters, I'm looking to set it up best way possible but there
> are some parameters which I'm not sure what they do (one of them being
> "ingress”).
> With the correct version of iproute2 installed, just issue “man tc-cake”.
> That’s the official documentation.
> Currently it doesn’t have the ingress keyword yet.  That’ll be fixed soon.
> > Also while reading on the bufferbloat.net Cake page I noticed a
> possible "fix" for BitTorrent (by setting it as "background",
> https://www.bufferbloat.net/projects/codel/wiki/Cake/#diffserv-support),
> I'm wondering if this can be done with Steam too?
> It’s possible, if you can figure out which traffic is Steam in the first
> place, and write filters to match on it.  This is complicated by the fact
> that Valve runs a sophisticated CDN to handle their rather impressive
> bandwidth load.
>  - Jonathan Morton
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> Cake at lists.bufferbloat.net
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